In writing the Little Plack Book, I spent a couple of days writing tests for Plack and applications at the PSGI level. Plack::Test occupies a strange level in the ecosystem. It's incredibly useful for what it does in selecting between a no-HTTP backend or any other PSGI-compatible handler, and it offers some degree of abstraction for making requests and getting results, but it's far too low level to write tests for complex applications.

When writing tests for a small Dancer application, I spent more time getting the Dancer environment set up well for testing than I did writing the tests. If I'd used Dancer::Test, I suspect I'd have made more progress more quickly.

I've had similar experiences with Catalyst and Catalyst::Test.

None of this surprises me—Catalyst and Dancer are one layer up the stack from Plack. Most of the interesting things you can test about a Catalyst or Dancer or Mojolicious or whatever application are properties expressed at the framework and application layers, not the plumbing layer of Plack.

Plack::Test seems best for testing middleware and other components which occupy the layer between PSGI and applications. Even so, something about its interface kept bothering me as I wrote tests and prose about the tests:

test_psgi $app, sub
{
    my $cb  = shift;

    my $res = $cb->( GET '/?have=tea;want=tea' );
    ok $res->is_success, 'Request should succeed when values match';
    is $res->decoded_content, 'ok',
        '... with descriptive success message';

    ...
};

The pattern of a special test function which takes a block of code is semi-common in the Test::* world; you can see it in Test::Exception and a lesser extent in Test::Fatal. The best example I've seen of this is Test::Routine, which uses this block syntax to help organize tests into named groups. A disciplined tester can use this to great effect to clarify what might otherwise become a big ball of muddy tests.

I like that Plack::Test does the hard work of redirecting requests to the app I want to test on whichever backend I want, so that I don't have to worry about setting up a testing deployment target. That part's great. The confusing part is:

my $cb  = shift;
my $res = $cb->( GET '/some_url' );

test_psgi takes a PSGI application and an anonymous function as its parameters, then invokes the anonymous function, passing a callback bound tothe context of the application. Inside the anonymous function (the block, not the callback), you invoke the callback and pass an HTTP::Request object (constructed manually or with a helper such as HTTP::Request::Common) and receive an HTTP::Response object.

Put that way, it's a lot more confusing than it is, if you're comfortable with the idea of first-class functions and closures and semi-fluent interfaces in Perl 5.

Even so, my $res = $cb->( $req ) just looks weird to me. It sticks out. It's visually different from all of the rest of the code. Everything else outside the test is the semi-fluent interface of anonymous subs or boring old method calls on objects.

In a discussion with Zbigniew Łukasiak, I suggested that I'd want an interface more like:

use Plack::Test;

plack_test 'Test description here' => sub
{
    my $app = shift;
    my $res = $app->get( '/', { have => 'tea', want => 'tea' } );

    ...
};

You can see the influence of Test::Routine. I don't know exactly how $app gets into the block, but this gives labeled subtests and the concomitant organization, it obviates the need to create HTTP::Request and HTTP::Response objects (or their Plack:: equivalents) manually, and everything in the block uses visually similar mechanisms.

The only hairy part is figuring out how to connect plack_test to the app while not multiplying hidden global variables or disallowing customization and decoration with other middleware. Compatibility with Plack::Builder is important, but I don't especially want to pass in $app myself manually.

Besides, to me the only obvious benefits over Test::WWW::Mechanize::PSGI are the subtest groupings. Mech has a huge advantage of providing many useful test assertion methods which grovel inside responses so I don't have to.

Maybe this is less my discomfort with one part of the useful-at-the-appropriate-level Plack::Test and more a plea to distinguish more clearly between various elements of Test::* modules, as several distinct categories of behavior exist:

• Setting up a testing environment
• Organizing test assertions
• Providing test assertions

We did a huge amount of work a long time ago with Test::Builder making sure that everything which wanted to provide test assertions could interact nicely, and we succeeded. Maybe it's time to consider ways to enable that composition at other layers of the Test::* stack.

Sometimes that ease moves the problem around, which reinforces the notion that the only two hard problems in computer science are naming and caching. To abuse that truism, once I've found a workable solution, the hard part is figuring out what to call it and how to make it available to other people.

Take the flash feature of Catalyst's Catalyst::Plugin::Session. It resembles the stash, in that you can store and retrieve information in and from the flash, but that data is only available until the first request which uses it. This is incredibly handy for user notifications, such as "You missed a required entry field!" or "Your interaction succeeded!", especially when combined with the Humane JS library.

My controller actions have a pattern:

sub edit :Chained( 'get_widget' ) :PathPart('edit') :Args(0)
{
    my ($self, $c) = @_;

    return unless lc $c->req->method eq 'post';

    my $params = $c->req->params;
    my $widget   = $c->stash->{widget};

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        push @{ $c->flash->{messages} }, 'Updated widget!';
    }
    catch { push @{ $c->flash->{errors} }, $_ };

    return $c->res->redirect(
        $c->uri_for( $c->controller( 'Widgets' )
          ->action_for( 'index' ) )
    );
}

Yet every time I write that code, it feels slightly wrong, as if I'm violating encapsulation by updating the variable behind the flash directly. It's also prone to typos and has the whiff of violating the Law of Demeter.

I prefer instead to write:

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        $c->add_message( 'Updated widget!' );
    }
    catch { $c->add_error( $_ ) };

... where my actions don't have to know about the internals of how the flash stores its data, where I don't have the possibility of stomping all over the array references accidentally, and where I can replace syntax (the grotty Perl 5 reference syntax!) with a method which describes my intent.

The simplest way to make this work is:

package Catalyst::Plugin::Session::FlashMethods;
# ABSTRACT: add flash-manipulation methods to Catalyst::Plugin::Session

use parent 'Catalyst::Plugin::Session';

use Modern::Perl;

sub add_message
{
    my $self = shift;
    push @{ $self->flash->{messages} }, @_;
}

sub add_error
{
    my $self = shift;
    push @{ $self->flash->{errors} }, @_;
}

1;

... and load it in my applications with:

use Catalyst::Plugin::ConfigLoader;
use Catalyst::Plugin::Static::Simple;
use Catalyst::Plugin::Session::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    ConfigLoader
    Static::Simple
    Session::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

This approach has (at least) two problems. First, while I'm happy to make this code available to other developers, I don't want to add any difficulties to use other plugins which may themselves extend or modify Catalyst::Plugin::Session.

Second, this code is awfully specific to my own uses. I believe those uses could help other people, but why solve a problem so specific when genericity and wider applicability are possible?

Rephrasing the problem might help.

I have a hash. I want named methods to store application-specific data in that hash. I would like the ability to customize that set of methods methods without hard-coding them, so as to produce a component that multiple people can reuse in multiple applications.

You can see why a big bag of untyped stuff (a hash) is useful.

What I really need is a way to say "My application will use these and only these specific elements of the flash, so please produce methods for them." Fortunately, I have one in MooseX::Role::Parameterized. The consumer of this code looks like:

package MyApp::Catalyst::Plugin::FlashMethods;
# ABSTRACT: role to add flash-manipulation methods to Catalyst app

use Moose;

extends 'Catalyst::Plugin::Session';
with 'Catalyst::Plugin::Role::FlashMethods'
    => { flash_elements => [qw( message error )] };

1;

... and it gets enabled in my Catalyst application with:

use MyApp::Catalyst::Plugin::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    -Debug
    ConfigLoader
    Static::Simple
    +MyApp::Catalyst::Plugin::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

... which consumes the parametric role:

package Catalyst::Plugin::Role::FlashMethods;

use MooseX::Role::Parameterized;

parameter 'flash_elements', isa => 'ArrayRef[Str]', required => 1;

role
{
    my $p = shift;

    for my $element (@{ $p->flash_elements })
    {
        method "add_${element}" => sub
        {
            my $self = shift;
            push @{ $self->flash->{ $element . 's' } }, @_;
        };
    }
};

1;

This code does have some naïve in it. In particular, it ought to use a smarter pluralization scheme. As well, the interface bothers me in two places. I'm not sure that the module's name is correct. I also don't particularly like that using this role means creating a new class of ~10 lines to make the code available as a Catalyst plugin (though how one might expand Catalyst's import() to understand how to reify a parametric role given the appropriate parameters is beyond my language design skills today).

Then again, my ~10 line plugin which consumes this role does work across my multiple Catalyst applications, at the cost of one more file and nine more lines of code altogether. The ratio of code per method decreases substantially with each new method I add, though.

I had originally intended to improve stash handling in this fashion, but but that's much more work. Neither Catalyst's core nor any other plugin I currently use rely on the presence of flash, so the scope of this work was much smaller. Even if they did, this approach does not prevent anything else from poking into the flash for good or ill.

Sometimes that ease moves the problem around, which reinforces the notion that the only two hard problems in computer science are naming and caching. To abuse that truism, once I've found a workable solution, the hard part is figuring out what to call it and how to make it available to other people.

Take the flash feature of Catalyst's Catalyst::Plugin::Session. It resembles the stash, in that you can store and retrieve information in and from the flash, but that data is only available until the first request which uses it. This is incredibly handy for user notifications, such as "You missed a required entry field!" or "Your interaction succeeded!", especially when combined with the Humane JS library.

My controller actions have a pattern:

sub edit :Chained( 'get_widget' ) :PathPart('edit') :Args(0)
{
    my ($self, $c) = @_;

    return unless lc $c->req->method eq 'post';

    my $params = $c->req->params;
    my $widget   = $c->stash->{widget};

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        push @{ $c->flash->{messages} }, 'Updated widget!';
    }
    catch { push @{ $c->flash->{errors} }, $_ };

    return $c->res->redirect(
        $c->uri_for( $c->controller( 'Widgets' )
          ->action_for( 'index' ) )
    );
}

Yet every time I write that code, it feels slightly wrong, as if I'm violating encapsulation by updating the variable behind the flash directly. It's also prone to typos and has the whiff of violating the Law of Demeter.

I prefer instead to write:

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        $c->add_message( 'Updated widget!' );
    }
    catch { $c->add_error( $_ ) };

... where my actions don't have to know about the internals of how the flash stores its data, where I don't have the possibility of stomping all over the array references accidentally, and where I can replace syntax (the grotty Perl 5 reference syntax!) with a method which describes my intent.

The simplest way to make this work is:

package Catalyst::Plugin::Session::FlashMethods;
# ABSTRACT: add flash-manipulation methods to Catalyst::Plugin::Session

use parent 'Catalyst::Plugin::Session';

use Modern::Perl;

sub add_message
{
    my $self = shift;
    push @{ $self->flash->{messages} }, @_;
}

sub add_error
{
    my $self = shift;
    push @{ $self->flash->{errors} }, @_;
}

1;

... and load it in my applications with:

use Catalyst::Plugin::ConfigLoader;
use Catalyst::Plugin::Static::Simple;
use Catalyst::Plugin::Session::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    ConfigLoader
    Static::Simple
    Session::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

This approach has (at least) two problems. First, while I'm happy to make this code available to other developers, I don't want to add any difficulties to use other plugins which may themselves extend or modify Catalyst::Plugin::Session.

Second, this code is awfully specific to my own uses. I believe those uses could help other people, but why solve a problem so specific when genericity and wider applicability are possible?

Rephrasing the problem might help.

I have a hash. I want named methods to store application-specific data in that hash. I would like the ability to customize that set of methods methods without hard-coding them, so as to produce a component that multiple people can reuse in multiple applications.

You can see why a big bag of untyped stuff (a hash) is useful.

What I really need is a way to say "My application will use these and only these specific elements of the flash, so please produce methods for them." Fortunately, I have one in MooseX::Role::Parameterized. The consumer of this code looks like:

package MyApp::Catalyst::Plugin::FlashMethods;
# ABSTRACT: role to add flash-manipulation methods to Catalyst app

use Moose;

extends 'Catalyst::Plugin::Session';
with 'Catalyst::Plugin::Role::FlashMethods'
    => { flash_elements => [qw( message error )] };

1;

... and it gets enabled in my Catalyst application with:

use MyApp::Catalyst::Plugin::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    -Debug
    ConfigLoader
    Static::Simple
    +MyApp::Catalyst::Plugin::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

... which consumes the parametric role:

package Catalyst::Plugin::Role::FlashMethods;

use MooseX::Role::Parameterized;

parameter 'flash_elements', isa => 'ArrayRef[Str]', required => 1;

role
{
    my $p = shift;

    for my $element (@{ $p->flash_elements })
    {
        method "add_${element}" => sub
        {
            my $self = shift;
            push @{ $self->flash->{ $element . 's' } }, @_;
        };
    }
};

1;

This code does have some naïve in it. In particular, it ought to use a smarter pluralization scheme. As well, the interface bothers me in two places. I'm not sure that the module's name is correct. I also don't particularly like that using this role means creating a new class of ~10 lines to make the code available as a Catalyst plugin (though how one might expand Catalyst's import() to understand how to reify a parametric role given the appropriate parameters is beyond my language design skills today).

Then again, my ~10 line plugin which consumes this role does work across my multiple Catalyst applications, at the cost of one more file and nine more lines of code altogether. The ratio of code per method decreases substantially with each new method I add, though.

I had originally intended to improve stash handling in this fashion, but but that's much more work. Neither Catalyst's core nor any other plugin I currently use rely on the presence of flash, so the scope of this work was much smaller. Even if they did, this approach does not prevent anything else from poking into the flash for good or ill.

Sometimes that ease moves the problem around, which reinforces the notion that the only two hard problems in computer science are naming and caching. To abuse that truism, once I've found a workable solution, the hard part is figuring out what to call it and how to make it available to other people.

Take the flash feature of Catalyst's Catalyst::Plugin::Session. It resembles the stash, in that you can store and retrieve information in and from the flash, but that data is only available until the first request which uses it. This is incredibly handy for user notifications, such as "You missed a required entry field!" or "Your interaction succeeded!", especially when combined with the Humane JS library.

My controller actions have a pattern:

sub edit :Chained( 'get_widget' ) :PathPart('edit') :Args(0)
{
    my ($self, $c) = @_;

    return unless lc $c->req->method eq 'post';

    my $params = $c->req->params;
    my $widget   = $c->stash->{widget};

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        push @{ $c->flash->{messages} }, 'Updated widget!';
    }
    catch { push @{ $c->flash->{errors} }, $_ };

    return $c->res->redirect(
        $c->uri_for( $c->controller( 'Widgets' )
          ->action_for( 'index' ) )
    );
}

Yet every time I write that code, it feels slightly wrong, as if I'm violating encapsulation by updating the variable behind the flash directly. It's also prone to typos and has the whiff of violating the Law of Demeter.

I prefer instead to write:

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        $c->add_message( 'Updated widget!' );
    }
    catch { $c->add_error( $_ ) };

... where my actions don't have to know about the internals of how the flash stores its data, where I don't have the possibility of stomping all over the array references accidentally, and where I can replace syntax (the grotty Perl 5 reference syntax!) with a method which describes my intent.

The simplest way to make this work is:

package Catalyst::Plugin::Session::FlashMethods;
# ABSTRACT: add flash-manipulation methods to Catalyst::Plugin::Session

use parent 'Catalyst::Plugin::Session';

use Modern::Perl;

sub add_message
{
    my $self = shift;
    push @{ $self->flash->{messages} }, @_;
}

sub add_error
{
    my $self = shift;
    push @{ $self->flash->{errors} }, @_;
}

1;

... and load it in my applications with:

use Catalyst::Plugin::ConfigLoader;
use Catalyst::Plugin::Static::Simple;
use Catalyst::Plugin::Session::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    ConfigLoader
    Static::Simple
    Session::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

This approach has (at least) two problems. First, while I'm happy to make this code available to other developers, I don't want to add any difficulties to use other plugins which may themselves extend or modify Catalyst::Plugin::Session.

Second, this code is awfully specific to my own uses. I believe those uses could help other people, but why solve a problem so specific when genericity and wider applicability are possible?

Rephrasing the problem might help.

I have a hash. I want named methods to store application-specific data in that hash. I would like the ability to customize that set of methods methods without hard-coding them, so as to produce a component that multiple people can reuse in multiple applications.

You can see why a big bag of untyped stuff (a hash) is useful.

What I really need is a way to say "My application will use these and only these specific elements of the flash, so please produce methods for them." Fortunately, I have one in MooseX::Role::Parameterized. The consumer of this code looks like:

package MyApp::Catalyst::Plugin::FlashMethods;
# ABSTRACT: role to add flash-manipulation methods to Catalyst app

use Moose;

extends 'Catalyst::Plugin::Session';
with 'Catalyst::Plugin::Role::FlashMethods'
    => { flash_elements => [qw( message error )] };

1;

... and it gets enabled in my Catalyst application with:

use MyApp::Catalyst::Plugin::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    -Debug
    ConfigLoader
    Static::Simple
    +MyApp::Catalyst::Plugin::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

... which consumes the parametric role:

package Catalyst::Plugin::Role::FlashMethods;

use MooseX::Role::Parameterized;

parameter 'flash_elements', isa => 'ArrayRef[Str]', required => 1;

role
{
    my $p = shift;

    for my $element (@{ $p->flash_elements })
    {
        method "add_${element}" => sub
        {
            my $self = shift;
            push @{ $self->flash->{ $element . 's' } }, @_;
        };
    }
};

1;

This code does have some naïve in it. In particular, it ought to use a smarter pluralization scheme. As well, the interface bothers me in two places. I'm not sure that the module's name is correct. I also don't particularly like that using this role means creating a new class of ~10 lines to make the code available as a Catalyst plugin (though how one might expand Catalyst's import() to understand how to reify a parametric role given the appropriate parameters is beyond my language design skills today).

Then again, my ~10 line plugin which consumes this role does work across my multiple Catalyst applications, at the cost of one more file and nine more lines of code altogether. The ratio of code per method decreases substantially with each new method I add, though.

I had originally intended to improve stash handling in this fashion, but but that's much more work. Neither Catalyst's core nor any other plugin I currently use rely on the presence of flash, so the scope of this work was much smaller. Even if they did, this approach does not prevent anything else from poking into the flash for good or ill.

Sometimes that ease moves the problem around, which reinforces the notion that the only two hard problems in computer science are naming and caching. To abuse that truism, once I've found a workable solution, the hard part is figuring out what to call it and how to make it available to other people.

Take the flash feature of Catalyst's Catalyst::Plugin::Session. It resembles the stash, in that you can store and retrieve information in and from the flash, but that data is only available until the first request which uses it. This is incredibly handy for user notifications, such as "You missed a required entry field!" or "Your interaction succeeded!", especially when combined with the Humane JS library.

My controller actions have a pattern:

sub edit :Chained( 'get_widget' ) :PathPart('edit') :Args(0)
{
    my ($self, $c) = @_;

    return unless lc $c->req->method eq 'post';

    my $params = $c->req->params;
    my $widget   = $c->stash->{widget};

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        push @{ $c->flash->{messages} }, 'Updated widget!';
    }
    catch { push @{ $c->flash->{errors} }, $_ };

    return $c->res->redirect(
        $c->uri_for( $c->controller( 'Widgets' )
          ->action_for( 'index' ) )
    );
}

Yet every time I write that code, it feels slightly wrong, as if I'm violating encapsulation by updating the variable behind the flash directly. It's also prone to typos and has the whiff of violating the Law of Demeter.

I prefer instead to write:

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        $c->add_message( 'Updated widget!' );
    }
    catch { $c->add_error( $_ ) };

... where my actions don't have to know about the internals of how the flash stores its data, where I don't have the possibility of stomping all over the array references accidentally, and where I can replace syntax (the grotty Perl 5 reference syntax!) with a method which describes my intent.

The simplest way to make this work is:

package Catalyst::Plugin::Session::FlashMethods;
# ABSTRACT: add flash-manipulation methods to Catalyst::Plugin::Session

use parent 'Catalyst::Plugin::Session';

use Modern::Perl;

sub add_message
{
    my $self = shift;
    push @{ $self->flash->{messages} }, @_;
}

sub add_error
{
    my $self = shift;
    push @{ $self->flash->{errors} }, @_;
}

1;

... and load it in my applications with:

use Catalyst::Plugin::ConfigLoader;
use Catalyst::Plugin::Static::Simple;
use Catalyst::Plugin::Session::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    ConfigLoader
    Static::Simple
    Session::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

This approach has (at least) two problems. First, while I'm happy to make this code available to other developers, I don't want to add any difficulties to use other plugins which may themselves extend or modify Catalyst::Plugin::Session.

Second, this code is awfully specific to my own uses. I believe those uses could help other people, but why solve a problem so specific when genericity and wider applicability are possible?

Rephrasing the problem might help.

I have a hash. I want named methods to store application-specific data in that hash. I would like the ability to customize that set of methods methods without hard-coding them, so as to produce a component that multiple people can reuse in multiple applications.

You can see why a big bag of untyped stuff (a hash) is useful.

What I really need is a way to say "My application will use these and only these specific elements of the flash, so please produce methods for them." Fortunately, I have one in MooseX::Role::Parameterized. The consumer of this code looks like:

package MyApp::Catalyst::Plugin::FlashMethods;
# ABSTRACT: role to add flash-manipulation methods to Catalyst app

use Moose;

extends 'Catalyst::Plugin::Session';
with 'Catalyst::Plugin::Role::FlashMethods'
    => { flash_elements => [qw( message error )] };

1;

... and it gets enabled in my Catalyst application with:

use MyApp::Catalyst::Plugin::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    -Debug
    ConfigLoader
    Static::Simple
    +MyApp::Catalyst::Plugin::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

... which consumes the parametric role:

package Catalyst::Plugin::Role::FlashMethods;

use MooseX::Role::Parameterized;

parameter 'flash_elements', isa => 'ArrayRef[Str]', required => 1;

role
{
    my $p = shift;

    for my $element (@{ $p->flash_elements })
    {
        method "add_${element}" => sub
        {
            my $self = shift;
            push @{ $self->flash->{ $element . 's' } }, @_;
        };
    }
};

1;

This code does have some naïve in it. In particular, it ought to use a smarter pluralization scheme. As well, the interface bothers me in two places. I'm not sure that the module's name is correct. I also don't particularly like that using this role means creating a new class of ~10 lines to make the code available as a Catalyst plugin (though how one might expand Catalyst's import() to understand how to reify a parametric role given the appropriate parameters is beyond my language design skills today).

Then again, my ~10 line plugin which consumes this role does work across my multiple Catalyst applications, at the cost of one more file and nine more lines of code altogether. The ratio of code per method decreases substantially with each new method I add, though.

I had originally intended to improve stash handling in this fashion, but but that's much more work. Neither Catalyst's core nor any other plugin I currently use rely on the presence of flash, so the scope of this work was much smaller. Even if they did, this approach does not prevent anything else from poking into the flash for good or ill.

Sometimes that ease moves the problem around, which reinforces the notion that the only two hard problems in computer science are naming and caching. To abuse that truism, once I've found a workable solution, the hard part is figuring out what to call it and how to make it available to other people.

Take the flash feature of Catalyst's Catalyst::Plugin::Session. It resembles the stash, in that you can store and retrieve information in and from the flash, but that data is only available until the first request which uses it. This is incredibly handy for user notifications, such as "You missed a required entry field!" or "Your interaction succeeded!", especially when combined with the Humane JS library.

My controller actions have a pattern:

sub edit :Chained( 'get_widget' ) :PathPart('edit') :Args(0)
{
    my ($self, $c) = @_;

    return unless lc $c->req->method eq 'post';

    my $params = $c->req->params;
    my $widget   = $c->stash->{widget};

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        push @{ $c->flash->{messages} }, 'Updated widget!';
    }
    catch { push @{ $c->flash->{errors} }, $_ };

    return $c->res->redirect(
        $c->uri_for( $c->controller( 'Widgets' )
          ->action_for( 'index' ) )
    );
}

Yet every time I write that code, it feels slightly wrong, as if I'm violating encapsulation by updating the variable behind the flash directly. It's also prone to typos and has the whiff of violating the Law of Demeter.

I prefer instead to write:

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        $c->add_message( 'Updated widget!' );
    }
    catch { $c->add_error( $_ ) };

... where my actions don't have to know about the internals of how the flash stores its data, where I don't have the possibility of stomping all over the array references accidentally, and where I can replace syntax (the grotty Perl 5 reference syntax!) with a method which describes my intent.

The simplest way to make this work is:

package Catalyst::Plugin::Session::FlashMethods;
# ABSTRACT: add flash-manipulation methods to Catalyst::Plugin::Session

use parent 'Catalyst::Plugin::Session';

use Modern::Perl;

sub add_message
{
    my $self = shift;
    push @{ $self->flash->{messages} }, @_;
}

sub add_error
{
    my $self = shift;
    push @{ $self->flash->{errors} }, @_;
}

1;

... and load it in my applications with:

use Catalyst::Plugin::ConfigLoader;
use Catalyst::Plugin::Static::Simple;
use Catalyst::Plugin::Session::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    ConfigLoader
    Static::Simple
    Session::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

This approach has (at least) two problems. First, while I'm happy to make this code available to other developers, I don't want to add any difficulties to use other plugins which may themselves extend or modify Catalyst::Plugin::Session.

Second, this code is awfully specific to my own uses. I believe those uses could help other people, but why solve a problem so specific when genericity and wider applicability are possible?

Rephrasing the problem might help.

I have a hash. I want named methods to store application-specific data in that hash. I would like the ability to customize that set of methods methods without hard-coding them, so as to produce a component that multiple people can reuse in multiple applications.

You can see why a big bag of untyped stuff (a hash) is useful.

What I really need is a way to say "My application will use these and only these specific elements of the flash, so please produce methods for them." Fortunately, I have one in MooseX::Role::Parameterized. The consumer of this code looks like:

package MyApp::Catalyst::Plugin::FlashMethods;
# ABSTRACT: role to add flash-manipulation methods to Catalyst app

use Moose;

extends 'Catalyst::Plugin::Session';
with 'Catalyst::Plugin::Role::FlashMethods'
    => { flash_elements => [qw( message error )] };

1;

... and it gets enabled in my Catalyst application with:

use MyApp::Catalyst::Plugin::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    -Debug
    ConfigLoader
    Static::Simple
    +MyApp::Catalyst::Plugin::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

... which consumes the parametric role:

package Catalyst::Plugin::Role::FlashMethods;

use MooseX::Role::Parameterized;

parameter 'flash_elements', isa => 'ArrayRef[Str]', required => 1;

role
{
    my $p = shift;

    for my $element (@{ $p->flash_elements })
    {
        method "add_${element}" => sub
        {
            my $self = shift;
            push @{ $self->flash->{ $element . 's' } }, @_;
        };
    }
};

1;

This code does have some naïve in it. In particular, it ought to use a smarter pluralization scheme. As well, the interface bothers me in two places. I'm not sure that the module's name is correct. I also don't particularly like that using this role means creating a new class of ~10 lines to make the code available as a Catalyst plugin (though how one might expand Catalyst's import() to understand how to reify a parametric role given the appropriate parameters is beyond my language design skills today).

Then again, my ~10 line plugin which consumes this role does work across my multiple Catalyst applications, at the cost of one more file and nine more lines of code altogether. The ratio of code per method decreases substantially with each new method I add, though.

I had originally intended to improve stash handling in this fashion, but but that's much more work. Neither Catalyst's core nor any other plugin I currently use rely on the presence of flash, so the scope of this work was much smaller. Even if they did, this approach does not prevent anything else from poking into the flash for good or ill.

Sometimes that ease moves the problem around, which reinforces the notion that the only two hard problems in computer science are naming and caching. To abuse that truism, once I've found a workable solution, the hard part is figuring out what to call it and how to make it available to other people.

Take the flash feature of Catalyst's Catalyst::Plugin::Session. It resembles the stash, in that you can store and retrieve information in and from the flash, but that data is only available until the first request which uses it. This is incredibly handy for user notifications, such as "You missed a required entry field!" or "Your interaction succeeded!", especially when combined with the Humane JS library.

My controller actions have a pattern:

sub edit :Chained( 'get_widget' ) :PathPart('edit') :Args(0)
{
    my ($self, $c) = @_;

    return unless lc $c->req->method eq 'post';

    my $params = $c->req->params;
    my $widget   = $c->stash->{widget};

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        push @{ $c->flash->{messages} }, 'Updated widget!';
    }
    catch { push @{ $c->flash->{errors} }, $_ };

    return $c->res->redirect(
        $c->uri_for( $c->controller( 'Widgets' )
          ->action_for( 'index' ) )
    );
}

Yet every time I write that code, it feels slightly wrong, as if I'm violating encapsulation by updating the variable behind the flash directly. It's also prone to typos and has the whiff of violating the Law of Demeter.

I prefer instead to write:

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        $c->add_message( 'Updated widget!' );
    }
    catch { $c->add_error( $_ ) };

... where my actions don't have to know about the internals of how the flash stores its data, where I don't have the possibility of stomping all over the array references accidentally, and where I can replace syntax (the grotty Perl 5 reference syntax!) with a method which describes my intent.

The simplest way to make this work is:

package Catalyst::Plugin::Session::FlashMethods;
# ABSTRACT: add flash-manipulation methods to Catalyst::Plugin::Session

use parent 'Catalyst::Plugin::Session';

use Modern::Perl;

sub add_message
{
    my $self = shift;
    push @{ $self->flash->{messages} }, @_;
}

sub add_error
{
    my $self = shift;
    push @{ $self->flash->{errors} }, @_;
}

1;

... and load it in my applications with:

use Catalyst::Plugin::ConfigLoader;
use Catalyst::Plugin::Static::Simple;
use Catalyst::Plugin::Session::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    ConfigLoader
    Static::Simple
    Session::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

This approach has (at least) two problems. First, while I'm happy to make this code available to other developers, I don't want to add any difficulties to use other plugins which may themselves extend or modify Catalyst::Plugin::Session.

Second, this code is awfully specific to my own uses. I believe those uses could help other people, but why solve a problem so specific when genericity and wider applicability are possible?

Rephrasing the problem might help.

I have a hash. I want named methods to store application-specific data in that hash. I would like the ability to customize that set of methods methods without hard-coding them, so as to produce a component that multiple people can reuse in multiple applications.

You can see why a big bag of untyped stuff (a hash) is useful.

What I really need is a way to say "My application will use these and only these specific elements of the flash, so please produce methods for them." Fortunately, I have one in MooseX::Role::Parameterized. The consumer of this code looks like:

package MyApp::Catalyst::Plugin::FlashMethods;
# ABSTRACT: role to add flash-manipulation methods to Catalyst app

use Moose;

extends 'Catalyst::Plugin::Session';
with 'Catalyst::Plugin::Role::FlashMethods'
    => { flash_elements => [qw( message error )] };

1;

... and it gets enabled in my Catalyst application with:

use MyApp::Catalyst::Plugin::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    -Debug
    ConfigLoader
    Static::Simple
    +MyApp::Catalyst::Plugin::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

... which consumes the parametric role:

package Catalyst::Plugin::Role::FlashMethods;

use MooseX::Role::Parameterized;

parameter 'flash_elements', isa => 'ArrayRef[Str]', required => 1;

role
{
    my $p = shift;

    for my $element (@{ $p->flash_elements })
    {
        method "add_${element}" => sub
        {
            my $self = shift;
            push @{ $self->flash->{ $element . 's' } }, @_;
        };
    }
};

1;

This code does have some naïve in it. In particular, it ought to use a smarter pluralization scheme. As well, the interface bothers me in two places. I'm not sure that the module's name is correct. I also don't particularly like that using this role means creating a new class of ~10 lines to make the code available as a Catalyst plugin (though how one might expand Catalyst's import() to understand how to reify a parametric role given the appropriate parameters is beyond my language design skills today).

Then again, my ~10 line plugin which consumes this role does work across my multiple Catalyst applications, at the cost of one more file and nine more lines of code altogether. The ratio of code per method decreases substantially with each new method I add, though.

I had originally intended to improve stash handling in this fashion, but but that's much more work. Neither Catalyst's core nor any other plugin I currently use rely on the presence of flash, so the scope of this work was much smaller. Even if they did, this approach does not prevent anything else from poking into the flash for good or ill.

Sometimes that ease moves the problem around, which reinforces the notion that the only two hard problems in computer science are naming and caching. To abuse that truism, once I've found a workable solution, the hard part is figuring out what to call it and how to make it available to other people.

Take the flash feature of Catalyst's Catalyst::Plugin::Session. It resembles the stash, in that you can store and retrieve information in and from the flash, but that data is only available until the first request which uses it. This is incredibly handy for user notifications, such as "You missed a required entry field!" or "Your interaction succeeded!", especially when combined with the Humane JS library.

My controller actions have a pattern:

sub edit :Chained( 'get_widget' ) :PathPart('edit') :Args(0)
{
    my ($self, $c) = @_;

    return unless lc $c->req->method eq 'post';

    my $params = $c->req->params;
    my $widget   = $c->stash->{widget};

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        push @{ $c->flash->{messages} }, 'Updated widget!';
    }
    catch { push @{ $c->flash->{errors} }, $_ };

    return $c->res->redirect(
        $c->uri_for( $c->controller( 'Widgets' )
          ->action_for( 'index' ) )
    );
}

Yet every time I write that code, it feels slightly wrong, as if I'm violating encapsulation by updating the variable behind the flash directly. It's also prone to typos and has the whiff of violating the Law of Demeter.

I prefer instead to write:

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        $c->add_message( 'Updated widget!' );
    }
    catch { $c->add_error( $_ ) };

... where my actions don't have to know about the internals of how the flash stores its data, where I don't have the possibility of stomping all over the array references accidentally, and where I can replace syntax (the grotty Perl 5 reference syntax!) with a method which describes my intent.

The simplest way to make this work is:

package Catalyst::Plugin::Session::FlashMethods;
# ABSTRACT: add flash-manipulation methods to Catalyst::Plugin::Session

use parent 'Catalyst::Plugin::Session';

use Modern::Perl;

sub add_message
{
    my $self = shift;
    push @{ $self->flash->{messages} }, @_;
}

sub add_error
{
    my $self = shift;
    push @{ $self->flash->{errors} }, @_;
}

1;

... and load it in my applications with:

use Catalyst::Plugin::ConfigLoader;
use Catalyst::Plugin::Static::Simple;
use Catalyst::Plugin::Session::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    ConfigLoader
    Static::Simple
    Session::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

This approach has (at least) two problems. First, while I'm happy to make this code available to other developers, I don't want to add any difficulties to use other plugins which may themselves extend or modify Catalyst::Plugin::Session.

Second, this code is awfully specific to my own uses. I believe those uses could help other people, but why solve a problem so specific when genericity and wider applicability are possible?

Rephrasing the problem might help.

I have a hash. I want named methods to store application-specific data in that hash. I would like the ability to customize that set of methods methods without hard-coding them, so as to produce a component that multiple people can reuse in multiple applications.

You can see why a big bag of untyped stuff (a hash) is useful.

What I really need is a way to say "My application will use these and only these specific elements of the flash, so please produce methods for them." Fortunately, I have one in MooseX::Role::Parameterized. The consumer of this code looks like:

package MyApp::Catalyst::Plugin::FlashMethods;
# ABSTRACT: role to add flash-manipulation methods to Catalyst app

use Moose;

extends 'Catalyst::Plugin::Session';
with 'Catalyst::Plugin::Role::FlashMethods'
    => { flash_elements => [qw( message error )] };

1;

... and it gets enabled in my Catalyst application with:

use MyApp::Catalyst::Plugin::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    -Debug
    ConfigLoader
    Static::Simple
    +MyApp::Catalyst::Plugin::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

... which consumes the parametric role:

package Catalyst::Plugin::Role::FlashMethods;

use MooseX::Role::Parameterized;

parameter 'flash_elements', isa => 'ArrayRef[Str]', required => 1;

role
{
    my $p = shift;

    for my $element (@{ $p->flash_elements })
    {
        method "add_${element}" => sub
        {
            my $self = shift;
            push @{ $self->flash->{ $element . 's' } }, @_;
        };
    }
};

1;

This code does have some naïve in it. In particular, it ought to use a smarter pluralization scheme. As well, the interface bothers me in two places. I'm not sure that the module's name is correct. I also don't particularly like that using this role means creating a new class of ~10 lines to make the code available as a Catalyst plugin (though how one might expand Catalyst's import() to understand how to reify a parametric role given the appropriate parameters is beyond my language design skills today).

Then again, my ~10 line plugin which consumes this role does work across my multiple Catalyst applications, at the cost of one more file and nine more lines of code altogether. The ratio of code per method decreases substantially with each new method I add, though.

I had originally intended to improve stash handling in this fashion, but but that's much more work. Neither Catalyst's core nor any other plugin I currently use rely on the presence of flash, so the scope of this work was much smaller. Even if they did, this approach does not prevent anything else from poking into the flash for good or ill.

Sometimes that ease moves the problem around, which reinforces the notion that the only two hard problems in computer science are naming and caching. To abuse that truism, once I've found a workable solution, the hard part is figuring out what to call it and how to make it available to other people.

Take the flash feature of Catalyst's Catalyst::Plugin::Session. It resembles the stash, in that you can store and retrieve information in and from the flash, but that data is only available until the first request which uses it. This is incredibly handy for user notifications, such as "You missed a required entry field!" or "Your interaction succeeded!", especially when combined with the Humane JS library.

My controller actions have a pattern:

sub edit :Chained( 'get_widget' ) :PathPart('edit') :Args(0)
{
    my ($self, $c) = @_;

    return unless lc $c->req->method eq 'post';

    my $params = $c->req->params;
    my $widget   = $c->stash->{widget};

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        push @{ $c->flash->{messages} }, 'Updated widget!';
    }
    catch { push @{ $c->flash->{errors} }, $_ };

    return $c->res->redirect(
        $c->uri_for( $c->controller( 'Widgets' )
          ->action_for( 'index' ) )
    );
}

Yet every time I write that code, it feels slightly wrong, as if I'm violating encapsulation by updating the variable behind the flash directly. It's also prone to typos and has the whiff of violating the Law of Demeter.

I prefer instead to write:

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        $c->add_message( 'Updated widget!' );
    }
    catch { $c->add_error( $_ ) };

... where my actions don't have to know about the internals of how the flash stores its data, where I don't have the possibility of stomping all over the array references accidentally, and where I can replace syntax (the grotty Perl 5 reference syntax!) with a method which describes my intent.

The simplest way to make this work is:

package Catalyst::Plugin::Session::FlashMethods;
# ABSTRACT: add flash-manipulation methods to Catalyst::Plugin::Session

use parent 'Catalyst::Plugin::Session';

use Modern::Perl;

sub add_message
{
    my $self = shift;
    push @{ $self->flash->{messages} }, @_;
}

sub add_error
{
    my $self = shift;
    push @{ $self->flash->{errors} }, @_;
}

1;

... and load it in my applications with:

use Catalyst::Plugin::ConfigLoader;
use Catalyst::Plugin::Static::Simple;
use Catalyst::Plugin::Session::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    ConfigLoader
    Static::Simple
    Session::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

This approach has (at least) two problems. First, while I'm happy to make this code available to other developers, I don't want to add any difficulties to use other plugins which may themselves extend or modify Catalyst::Plugin::Session.

Second, this code is awfully specific to my own uses. I believe those uses could help other people, but why solve a problem so specific when genericity and wider applicability are possible?

Rephrasing the problem might help.

I have a hash. I want named methods to store application-specific data in that hash. I would like the ability to customize that set of methods methods without hard-coding them, so as to produce a component that multiple people can reuse in multiple applications.

You can see why a big bag of untyped stuff (a hash) is useful.

What I really need is a way to say "My application will use these and only these specific elements of the flash, so please produce methods for them." Fortunately, I have one in MooseX::Role::Parameterized. The consumer of this code looks like:

package MyApp::Catalyst::Plugin::FlashMethods;
# ABSTRACT: role to add flash-manipulation methods to Catalyst app

use Moose;

extends 'Catalyst::Plugin::Session';
with 'Catalyst::Plugin::Role::FlashMethods'
    => { flash_elements => [qw( message error )] };

1;

... and it gets enabled in my Catalyst application with:

use MyApp::Catalyst::Plugin::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    -Debug
    ConfigLoader
    Static::Simple
    +MyApp::Catalyst::Plugin::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

... which consumes the parametric role:

package Catalyst::Plugin::Role::FlashMethods;

use MooseX::Role::Parameterized;

parameter 'flash_elements', isa => 'ArrayRef[Str]', required => 1;

role
{
    my $p = shift;

    for my $element (@{ $p->flash_elements })
    {
        method "add_${element}" => sub
        {
            my $self = shift;
            push @{ $self->flash->{ $element . 's' } }, @_;
        };
    }
};

1;

This code does have some naïve in it. In particular, it ought to use a smarter pluralization scheme. As well, the interface bothers me in two places. I'm not sure that the module's name is correct. I also don't particularly like that using this role means creating a new class of ~10 lines to make the code available as a Catalyst plugin (though how one might expand Catalyst's import() to understand how to reify a parametric role given the appropriate parameters is beyond my language design skills today).

Then again, my ~10 line plugin which consumes this role does work across my multiple Catalyst applications, at the cost of one more file and nine more lines of code altogether. The ratio of code per method decreases substantially with each new method I add, though.

I had originally intended to improve stash handling in this fashion, but but that's much more work. Neither Catalyst's core nor any other plugin I currently use rely on the presence of flash, so the scope of this work was much smaller. Even if they did, this approach does not prevent anything else from poking into the flash for good or ill.

Sometimes that ease moves the problem around, which reinforces the notion that the only two hard problems in computer science are naming and caching. To abuse that truism, once I've found a workable solution, the hard part is figuring out what to call it and how to make it available to other people.

Take the flash feature of Catalyst's Catalyst::Plugin::Session. It resembles the stash, in that you can store and retrieve information in and from the flash, but that data is only available until the first request which uses it. This is incredibly handy for user notifications, such as "You missed a required entry field!" or "Your interaction succeeded!", especially when combined with the Humane JS library.

My controller actions have a pattern:

sub edit :Chained( 'get_widget' ) :PathPart('edit') :Args(0)
{
    my ($self, $c) = @_;

    return unless lc $c->req->method eq 'post';

    my $params = $c->req->params;
    my $widget   = $c->stash->{widget};

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        push @{ $c->flash->{messages} }, 'Updated widget!';
    }
    catch { push @{ $c->flash->{errors} }, $_ };

    return $c->res->redirect(
        $c->uri_for( $c->controller( 'Widgets' )
          ->action_for( 'index' ) )
    );
}

Yet every time I write that code, it feels slightly wrong, as if I'm violating encapsulation by updating the variable behind the flash directly. It's also prone to typos and has the whiff of violating the Law of Demeter.

I prefer instead to write:

    try
    {
        $widget->$_( $params->{$_} ) for $widget->editable_fields;
        $widget->update;
        $c->add_message( 'Updated widget!' );
    }
    catch { $c->add_error( $_ ) };

... where my actions don't have to know about the internals of how the flash stores its data, where I don't have the possibility of stomping all over the array references accidentally, and where I can replace syntax (the grotty Perl 5 reference syntax!) with a method which describes my intent.

The simplest way to make this work is:

package Catalyst::Plugin::Session::FlashMethods;
# ABSTRACT: add flash-manipulation methods to Catalyst::Plugin::Session

use parent 'Catalyst::Plugin::Session';

use Modern::Perl;

sub add_message
{
    my $self = shift;
    push @{ $self->flash->{messages} }, @_;
}

sub add_error
{
    my $self = shift;
    push @{ $self->flash->{errors} }, @_;
}

1;

... and load it in my applications with:

use Catalyst::Plugin::ConfigLoader;
use Catalyst::Plugin::Static::Simple;
use Catalyst::Plugin::Session::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    ConfigLoader
    Static::Simple
    Session::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

This approach has (at least) two problems. First, while I'm happy to make this code available to other developers, I don't want to add any difficulties to use other plugins which may themselves extend or modify Catalyst::Plugin::Session.

Second, this code is awfully specific to my own uses. I believe those uses could help other people, but why solve a problem so specific when genericity and wider applicability are possible?

Rephrasing the problem might help.

I have a hash. I want named methods to store application-specific data in that hash. I would like the ability to customize that set of methods methods without hard-coding them, so as to produce a component that multiple people can reuse in multiple applications.

You can see why a big bag of untyped stuff (a hash) is useful.

What I really need is a way to say "My application will use these and only these specific elements of the flash, so please produce methods for them." Fortunately, I have one in MooseX::Role::Parameterized. The consumer of this code looks like:

package MyApp::Catalyst::Plugin::FlashMethods;
# ABSTRACT: role to add flash-manipulation methods to Catalyst app

use Moose;

extends 'Catalyst::Plugin::Session';
with 'Catalyst::Plugin::Role::FlashMethods'
    => { flash_elements => [qw( message error )] };

1;

... and it gets enabled in my Catalyst application with:

use MyApp::Catalyst::Plugin::FlashMethods;
use Catalyst::Plugin::Session::State::Cookie;
use Catalyst::Plugin::Session::Store::FastMmap;

use Catalyst qw/
    -Debug
    ConfigLoader
    Static::Simple
    +MyApp::Catalyst::Plugin::FlashMethods
    Session::State::Cookie
    Session::Store::FastMmap
/;

... which consumes the parametric role:

package Catalyst::Plugin::Role::FlashMethods;

use MooseX::Role::Parameterized;

parameter 'flash_elements', isa => 'ArrayRef[Str]', required => 1;

role
{
    my $p = shift;

    for my $element (@{ $p->flash_elements })
    {
        method "add_${element}" => sub
        {
            my $self = shift;
            push @{ $self->flash->{ $element . 's' } }, @_;
        };
    }
};

1;

This code does have some naïve in it. In particular, it ought to use a smarter pluralization scheme. As well, the interface bothers me in two places. I'm not sure that the module's name is correct. I also don't particularly like that using this role means creating a new class of ~10 lines to make the code available as a Catalyst plugin (though how one might expand Catalyst's import() to understand how to reify a parametric role given the appropriate parameters is beyond my language design skills today).

Then again, my ~10 line plugin which consumes this role does work across my multiple Catalyst applications, at the cost of one more file and nine more lines of code altogether. The ratio of code per method decreases substantially with each new method I add, though.

I had originally intended to improve stash handling in this fashion, but but that's much more work. Neither Catalyst's core nor any other plugin I currently use rely on the presence of flash, so the scope of this work was much smaller. Even if they did, this approach does not prevent anything else from poking into the flash for good or ill.