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;

Delegating to CodeRefs¶

You can delegate to coderefs:

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

Delegating to Named Methods¶

The Sub::HandlesVia::HandlerLibrary::Blessed handler library allows you to delegate to named methods of a blessed object.

     isa         => InstanceOf['HTTP::Tiny'],
     handles_via => 'Blessed',
     handles     => {
       'http_get'   => 'get',
       'http_post'  => 'post',
     },

However, in Moo, Moose, Mouse, and Mite, this kind of delegation is baked in, so you don't even need Sub::HandlesVia!

     isa         => InstanceOf['HTTP::Tiny'],
     handles     => {
       'http_get'   => 'get',
       'http_post'  => 'post',
     },

Still, the Sub::HandlesVia::HandlerLibrary::Blessed handler library may still be useful if you wish to use other Sub::HandlesVia features like chaining, or if you're using a different OO toolkit.

An example of combining delegation to named methods with "native trait" style delegation... let's say "FoodList" is a class where instances are blessed arrayrefs of strings.

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

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

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

But because "find_healthiest" isn't one of the methods offered by Sub::HandlesVia::HandlerList::Array, Sub::HandlesVia assumes you want to call it on the arrayref like a proper method, so "$kitchen->find_healthiest_food" does this:

  $kitchen->food->find_healthiest

It can be useful to be explicit about which methods you wish to delegate to a "native trait" style array and which are named methods to be called on a blessed object:

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

See "Delegating to Multiple Handler Libraries".

Curried Arguments¶

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 ],
     },

Looser Argument Checking¶

Sub::HandlesVia tries to be strict by default. For example, if your attribute specifies "isa => ArrayRef[Int]" then your method which delegates to "push" will check that its arguments are integers.

You can tell it to be less rigourous checking method arguments using the "~" prefix:

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

Delegating to Multiple Handler Libraries¶

Sometimes you may wish to pick methods to delegate to from multiple handler libraries. This is possible by setting "handles_via" to an arrayref.

    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 "%{}".

In particular, the Sub::HandlesVia::HandlerLibrary::Scalar library often makes sense to combine with the other libraries because strings, integers, numbers, booleans, and even arrayrefs, hashrefs, and coderefs, are all scalars.

Sometimes a method name 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_by_index => 'Array->get',
       get_by_key   => 'Hash->get',
     }