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Michael G Schwern > perl5i > perl5i::Signature


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perl5i::Signature - Representing what parameters a subroutine accepts


    func hello( $greeting, $place ) { say "$greeting, $place" }

    my $code = \&hello;
    my $signature = $code->signature;

    say $signature->num_positional_params;  # 2
    say $signature->is_method;   # false


A Signature is a representation of what parameters a subroutine accepts. Each subroutine defined with func or method will have a signature associated with it. You can get at it by calling the signature method on the code reference. See "Signature Introspection" in perl5i for more details.

Subroutines declared with Perl's built in sub will have no signature.



    my $params = $sig->params;

An array ref of the parameters a subroutine takes in the order it takes them. Currently they are just strings. In the future they will be string overloaded objects.


    my $params = $sig->positional_params;

Like $sig->params but it is just the positional parameters.

In the future there will be named parameters.


    my $num_positional_params = $sig->num_positional_params;

The number of named parameters the subroutine takes.

In the future there will be named parameters. For the purposes of determining how many arguments a function takes, it is most useful to look just at the positional ones.

This is mostly an optimization for $sig->positional_params->size.


    my $params = $sig->as_string;

The original signature string.


    my $invocant = $sig->invocant;

The invocant is the object or class a method is called on. invocant will return the parameter which contains this, by default it is $self on a method, and nothing a regular subroutine.


    my $is_method = $sig->is_method;

Returns if the subroutine was declared as a method.


Signature objects are string overloaded to return as_string. They are also always true to avoid objects taking no parameters from being confused with subroutines with no signatures.

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