Syntax::Feature::Sugar::Callbacks - Add sugar for declarative method callbacks


version 0.002


    use AnythingExportingMethodModifiers;
    use syntax 'sugar/callbacks' => {
        -callbacks => {
            after   => {},
            before  => {},
            around  => { -before => ['$orig'] },

    after  foo ($n) { $self->something($n) }
    before bar ($n) { $self->something($n) }
    around baz ($n) { $self->something($self->$orig($n)) }


You probably won't use this extension directly. That's why it doesn't even have an import method. Its main reasoning is the ability to provide on-the-fly sugar for method declarators, most commonly before, after and around. This extension will directly dispatch to the original subroutine, and requires these to be setup before-hand. Currently, all callbacks will first receive the name of the declared method, followed by the code reference.

Note that no cleanup of the original handlers will be performed. This is up to the exporting library or the user.



    $class->install( %arguments )

Called by syntax (or others) to install this extension into a namespace.


All declarations must currently be in one of the forms

    <keyword> <name> (<signature>) { <body> }
    <keyword> <name> { <body> }

The keyword is the name of the declared callback. The name can either be an identifier like you'd give to sub, or a double-quoted string if you want the name to be dynamic:

    after "$name" ($arg) { ... }

The signature, if specified, should be in one of the following forms:

    ($foo, $bar)
    ($class: $foo, $bar)

Variables before : will be used as replacement for the invocant. Parameters specified via -before and -middle will always be included.

The statement will automatically terminate after the block. The return value will be whatever the original callback returns.

You can supply subroutine attributes right before the block.



Defaults to $self, but you might want to change this for very specialized classes.


This is the set of callbacks that should be setup. It should be a hash reference using callback names as keys and hash references of options as values. Possible per-callback options are


An array reference of variable names that come before the invocant. A typical example would be the original code reference in around method modifiers.


An array reference of variable names that come after the invocants, but before the parameters specified in the signature. Use this if the code reference declared with the construct will receive a constant parameter. There is no current way to override this in the signature on a per-construct basis.


An array reference of variable names that are used when no signature was provided. An empty signature will not lead to the defaults being used.


By default, anonymous constructs will not automatically terminate the statement after the code block. If this option is set to a true value, all uses of the construct will be terminated.


If set to a true value, anonymous versions of this construct can be declared. If no name was specified, only the code reference will be passed on to the callback.


If set to a true value, a name will not be expected after the keyword and before the signature.



Please report any bugs or feature requests to or through the web interface at:


Robert 'phaylon' Sedlacek <>


This software is copyright (c) 2011 by Robert 'phaylon' Sedlacek.

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