Sub::HandlesVia(3)

NAME
Sub::HandlesVia - alternative handles_via implementation

SYNOPSIS
 package Kitchen {
   use Moo;
   use Sub::HandlesVia;
   use Types::Standard qw( ArrayRef Str );

   has food => (
     is          => 'ro',
     isa         => ArrayRef[Str],
     handles_via => 'Array',
     default     => sub { [] },
     handles     => {
       'add_food'    => 'push',
       'find_food'   => 'grep',
     },
   );
 }

 my $kitchen = Kitchen->new;
 $kitchen->add_food('Bacon');
 $kitchen->add_food('Eggs');
 $kitchen->add_food('Sausages');
 $kitchen->add_food('Beans');

 my @foods = $kitchen->find_food(sub { /^B/i });

DESCRIPTION
If you've used Moose's native attribute traits, or MooX::HandlesVia before, you should have a fairly good idea what this does.

Why re-invent the wheel? Well, this is an implementation that should work okay with Moo, Moose, Mouse, and any other OO toolkit you throw at it. One ring to rule them all, so to speak.

Also, unlike MooX::HandlesVia, it honours type constraints, plus it doesn't have the limitation that it can't mutate non-reference values.

  Using with Moo
You should be able to use it as a drop-in replacement for MooX::HandlesVia.

 package Kitchen {
   use Moo;
   use Sub::HandlesVia;
   use Types::Standard qw( ArrayRef Str );

   has food => (
     is          => 'ro',
     isa         => ArrayRef[Str],
     handles_via => 'Array',
     default     => sub { [] },
     handles     => {
       'add_food'    => 'push',
       'find_food'   => 'grep',
     },
   );
 }

  Using with Mouse
It works the same as Moo basically.

 package Kitchen {
   use Mouse;
   use Sub::HandlesVia;
   use Types::Standard qw( ArrayRef Str );

   has food => (
     is          => 'ro',
     isa         => ArrayRef[Str],
     handles_via => 'Array',
     default     => sub { [] },
     handles     => {
       'add_food'    => 'push',
       'find_food'   => 'grep',
     },
   );
 }

You are not forced to use Types::Standard. Mouse native types should work fine.

 package Kitchen {
   use Mouse;
   use Sub::HandlesVia;

   has food => (
     is          => 'ro',
     isa         => 'ArrayRef[Str]',
     handles_via => 'Array',
     default     => sub { [] },
     handles     => {
       'add_food'    => 'push',
       'find_food'   => 'grep',
     },
   );
 }

Sub::HandlesVia will also recognize MooseX::NativeTraits-style traits. It will jump in and handle them before MooseX::NativeTraits notices!

 package Kitchen {
   use Mouse;
   use Sub::HandlesVia;

   has food => (
     is          => 'ro',
     isa         => 'ArrayRef[Str]',
     traits      => ['Array'],
     default     => sub { [] },
     handles     => {
       'add_food'    => 'push',
       'find_food'   => 'grep',
     },
   );
 }

(If you have a mouse in your kitchen though, that might not be very hygienic.)

  Using with Moose
It works the same as Mouse basically.

 package Kitchen {
   use Moose;
   use Sub::HandlesVia;
   use Types::Standard qw( ArrayRef Str );

   has food => (
     is          => 'ro',
     isa         => ArrayRef[Str],
     handles_via => 'Array',
     default     => sub { [] },
     handles     => {
       'add_food'    => 'push',
       'find_food'   => 'grep',
     },
   );
 }

You are not forced to use Types::Standard. Moose native types should work fine.

 package Kitchen {
   use Moose;
   use Sub::HandlesVia;

   has food => (
     is          => 'ro',
     isa         => 'ArrayRef[Str]',
     handles_via => 'Array',
     default     => sub { [] },
     handles     => {
       'add_food'    => 'push',
       'find_food'   => 'grep',
     },
   );
 }

Sub::HandlesVia will also recognize native-traits-style traits. It will jump in and handle them before Moose notices!

 package Kitchen {
   use Moose;
   use Sub::HandlesVia;

   has food => (
     is          => 'ro',
     isa         => 'ArrayRef[Str]',
     traits      => ['Array'],
     default     => sub { [] },
     handles     => {
       'add_food'    => 'push',
       'find_food'   => 'grep',
     },
   );
 }

(If you have a moose in your kitchen, that might be even worse than the mouse.)

  Using with Anything
For Moose and Mouse, Sub::HandlesVia can use their metaobject protocols to grab an attribute's definition and install the methods it needs to. For Moo, it can wrap "has" and do its stuff that way. For other classes, you need to be more explicit and tell it what methods to delegate to what attributes.

 package Kitchen {
   use Class::Tiny {
     food => sub { [] },
   };

   use Sub::HandlesVia qw( delegations );

   delegations(
     attribute   => 'food'
     handles_via => 'Array',
     handles     => {
       'add_food'    => 'push',
       'find_food'   => 'grep',
     },
   );
 }

Setting "attribute" to "food" means that when Sub::HandlesVia needs to get the food list, it will call "$kitchen->food" and when it needs to set the food list, it will call "$kitchen->food($value)". If you have separate getter and setter methods, just do:

     attribute   => [ 'get_food', 'set_food' ],

Or if you don't have any accessors and want Sub::HandlesVia to directly access the underlying hashref:

     attribute   => '{food}',

Or maybe you have a setter, but want to use hashref access for the getter:

     attribute   => [ '{food}', 'set_food' ],

Or maybe you still want direct access for the getter, but your object is a blessed arrayref instead of a blessed hashref:

     attribute   => [ '[7]', 'set_food' ],

Or maybe your needs are crazy unique:

     attribute   => [ \&getter, \&setter ],

The coderefs are passed the instance as their first argument, and the setter is also passed a value to set.

Really, I don't think there's any object system that this won't work for!

If you supply an arrayref with a getter and setter, it's also possible to supply a third argument which is a coderef or string which will be called as a method if needing to "reset" the value. This can be thought of like a default or builder.

(The "delegations" function can be imported into Moo/Mouse/Moose classes too, in which case the "attribute" needs to be the same attribute name you passed to "has". You cannot use a arrayref, coderef, hash key, or array index.)

  What methods can be delegated to?
The following table compares Sub::HandlesVia with Data::Perl, Moose native traits, and MouseX::NativeTraits.

  Array ===========================================
            accessor : SubHV  DataP  Moose  Mouse
                 all : SubHV  DataP
            all_true : SubHV
                 any : SubHV                Mouse
               apply : SubHV                Mouse
               clear : SubHV  DataP  Moose  Mouse
               count : SubHV  DataP  Moose  Mouse
              delete : SubHV  DataP  Moose  Mouse
            elements : SubHV  DataP  Moose  Mouse
               fetch :                      Mouse  (alias: get)
               first : SubHV  DataP  Moose  Mouse
         first_index : SubHV  DataP  Moose
             flatten : SubHV  DataP
        flatten_deep : SubHV  DataP
            for_each : SubHV                Mouse
       for_each_pair : SubHV                Mouse
                 get : SubHV  DataP  Moose  Mouse
                grep : SubHV  DataP  Moose  Mouse
                head : SubHV  DataP
              insert : SubHV  DataP  Moose  Mouse
            is_empty : SubHV  DataP  Moose  Mouse
                join : SubHV  DataP  Moose  Mouse
                 map : SubHV  DataP  Moose  Mouse
                 max : SubHV
              maxstr : SubHV
                 min : SubHV
              minstr : SubHV
            natatime : SubHV  DataP  Moose
        not_all_true : SubHV
           pairfirst : SubHV
            pairgrep : SubHV
            pairkeys : SubHV
             pairmap : SubHV
               pairs : SubHV
          pairvalues : SubHV
         pick_random : SubHV
                 pop : SubHV  DataP  Moose  Mouse
               print : SubHV  DataP
             product : SubHV
                push : SubHV  DataP  Moose  Mouse
              reduce : SubHV  DataP  Moose  Mouse
          reductions : SubHV
              remove :                      Mouse  (alias: delete)
               reset : SubHV
             reverse : SubHV  DataP
              sample : SubHV
                 set : SubHV  DataP  Moose  Mouse
       shallow_clone : SubHV  DataP  Moose
               shift : SubHV  DataP  Moose  Mouse
             shuffle : SubHV  DataP  Moose  Mouse
    shuffle_in_place : SubHV
                sort : SubHV  DataP  Moose  Mouse
             sort_by :                      Mouse  (sort)
       sort_in_place : SubHV  DataP  Moose  Mouse
    sort_in_place_by :                      Mouse  (sort_in_place)
              splice : SubHV  DataP  Moose  Mouse
               store :                      Mouse  (alias: set)
                 sum : SubHV
                tail : SubHV  DataP
                uniq : SubHV  DataP  Moose  Mouse
       uniq_in_place : SubHV
             uniqnum : SubHV
    uniqnum_in_place : SubHV
             uniqstr : SubHV
    uniqstr_in_place : SubHV
             unshift : SubHV  DataP  Moose  Mouse

  Bool ============================================
                 not : SubHV  DataP  Moose  Mouse
               reset : SubHV
                 set : SubHV  DataP  Moose  Mouse
              toggle : SubHV  DataP  Moose  Mouse
               unset : SubHV  DataP  Moose  Mouse

  Code ============================================
             execute : SubHV  DataP  Moose  Mouse
      execute_method : SubHV         Moose  Mouse

  Counter =========================================
                 dec : SubHV  DataP  Moose  Mouse
                 inc : SubHV  DataP  Moose  Mouse
               reset : SubHV  DataP  Moose  Mouse
                 set : SubHV         Moose  Mouse

  Hash ============================================
            accessor : SubHV  DataP  Moose  Mouse
                 all : SubHV  DataP
               clear : SubHV  DataP  Moose  Mouse
               count : SubHV  DataP  Moose  Mouse
             defined : SubHV  DataP  Moose  Mouse
              delete : SubHV  DataP  Moose  Mouse
            elements : SubHV  DataP  Moose  Mouse
              exists : SubHV  DataP  Moose  Mouse
               fetch :                      Mouse  (alias: get)
        for_each_key : SubHV                Mouse
       for_each_pair : SubHV                Mouse
      for_each_value : SubHV                Mouse
                 get : SubHV  DataP  Moose  Mouse
            is_empty : SubHV  DataP  Moose  Mouse
                keys : SubHV  DataP  Moose  Mouse
                  kv : SubHV  DataP  Moose  Mouse
               reset : SubHV
                 set : SubHV  DataP  Moose  Mouse
       shallow_clone : SubHV  DataP  Moose
         sorted_keys : SubHV                Mouse
               store :                      Mouse  (alias: set)
              values : SubHV  DataP  Moose  Mouse

  Number ==========================================
                 abs : SubHV  DataP  Moose  Mouse
                 add : SubHV  DataP  Moose  Mouse
                 div : SubHV  DataP  Moose  Mouse
                 get : SubHV
                 mod : SubHV  DataP  Moose  Mouse
                 mul : SubHV  DataP  Moose  Mouse
                 set : SubHV         Moose
                 sub : SubHV  DataP  Moose  Mouse

  String ==========================================
              append : SubHV  DataP  Moose  Mouse
               chomp : SubHV  DataP  Moose  Mouse
                chop : SubHV  DataP  Moose  Mouse
               clear : SubHV  DataP  Moose  Mouse
                 get : SubHV
                 inc : SubHV  DataP  Moose  Mouse
              length : SubHV  DataP  Moose  Mouse
               match : SubHV  DataP  Moose  Mouse
             prepend : SubHV  DataP  Moose  Mouse
             replace : SubHV  DataP  Moose  Mouse
    replace_globally : SubHV                Mouse
               reset : SubHV
                 set : SubHV
              substr : SubHV  DataP  Moose  Mouse

  Method Chaining
Say you have the following

     handles_via => 'Array',
     handles     => {
       'add_food'    => 'push',
       'find_food'   => 'grep',
       'remove_food' => 'pop',
     },

Now "$kitchen->remove_food" will remove the last food on the list and return it. But what if we don't care about what food was removed? We just want to remove the food and discard it. You can do this:

     handles_via => 'Array',
     handles     => {
       'add_food'    => 'push',
       'find_food'   => 'grep',
       'remove_food' => 'pop...',
     },

Now the "remove_food" method will return the kitchen object instead of returning the food. This makes it suitable for chaining method calls:

  # remove the three most recent foods
  $kitchen->remove_food->remove_food->remove_food;

  Hand Waving
Sub::HandlesVia tries to be strict by default, but you can tell it to be less rigourous checking method arguments, etc using the "~" prefix:

     handles_via => 'Array',
     handles     => {
       'find_food'   => '~grep',
     },

  CodeRefs
You can delegate to coderefs:

     handles_via => 'Array',
     handles    => {
       'find_healthiest' => sub { my $foods = shift; ... },
     }

  Named Methods
Let's say "FoodList" is a class where instances are blessed arrayrefs of strings.

     isa         => InstanceOf['FoodList'],
     handles_via => 'Array',
     handles     => {
       'find_food'             => 'grep',
       'find_healthiest_food'  => 'find_healthiest',
     },

Now "$kitchen->find_food($coderef)" does this (which breaks encapsulation of course):

  my @result = grep $coderef->(), @{ $kitchen->food };

And "$kitchen->find_healthiest_food" does this:

  $kitchen->food->find_healthiest

Basically, because "find_healthiest" isn't one of the methods offered by Sub::HandlesVia::HandlerList::Array, it assumes you want to call it on the arrayref like a proper method.

  Currying Favour
All this talk of food is making me hungry, but as much as I'd like to eat a curry right now, that's not the kind of currying we're talking about.

     handles_via => 'Array',
     handles     => {
       'get_food'   => 'get',
     },

"$kitchen->get_food(0)" will return the first item on the list. "$kitchen->get_food(1)" will return the second item on the list. And so on.

     handles_via => 'Array',
     handles     => {
       'first_food'   => [ 'get' => 0 ],
       'second_food'  => [ 'get' => 1 ],
     },

I think you already know what this does. Right?

And yes, currying works with coderefs.

     handles_via => 'Array',
     handles     => {
       'blargy'       => [ sub { ... }, @curried ],
     },

  Pick and Mix
    isa         => ArrayRef|HashRef,
    handles_via => [ 'Array', 'Hash' ],
    handles     => {
      the_keys     => 'keys',
      ship_shape   => 'sort_in_place',
    }

Here you have an attribute which might be an arrayref or a hashref. When it's an arrayref, "$object->ship_shape" will work nicely, but "$object->the_keys" will fail badly.

Still, this sort of thing can kind of make sense if you have an object that overloads both "@{}" and "%{}".

Sometime a method will be ambiguous. For example, there's a "get" method for both hashes and arrays. In this case, the array one will win because you listed it first in "handles_via".

But you can be specific:

    isa         => ArrayRef|HashRef,
    handles_via => [ 'Array', 'Hash' ],
    handles     => {
      get_foo => 'Array->get',
      get_bar => 'Hash->get',
    }

BUGS
Please report any bugs to <http://rt.cpan.org/Dist/Display.html?Queue=Sub-HandlesVia>.

(There are known bugs for Moose native types that do coercion.)

SEE ALSO
Moose, MouseX::NativeTraits, Data::Perl, MooX::HandlesVia.

AUTHOR
Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE
This software is copyright (c) 2020 by Toby Inkster.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

DISCLAIMER OF WARRANTIES
THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.