---
name: "Function::Parameters::Info"
section: "3pm"
platform: "linux"
package: "libfunction-parameters-perl"
version: "2.002005-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/Function::Parameters::Info"
---

# Function::Parameters::Info(3pm)

Information about parameter lists

## NAME

Function::Parameters::Info - Information about parameter lists

## SYNOPSIS

```
    use Function::Parameters;
    fun foo($x, $y, :$hello, :$world = undef) {}
    my $info = Function::Parameters::info \&foo;
    my @p0 = $info->invocants;            # ()
    my @p1 = $info->positional_required;  # ('$x', '$y')
    my @p2 = $info->positional_optional;  # ()
    my @p3 = $info->named_required;       # ('$hello')
    my @p4 = $info->named_optional;       # ('$world')
    my $p5 = $info->slurpy;               # undef
    my $min = $info->args_min;  # 4
    my $max = $info->args_max;  # inf
    my @invocants = Function::Parameters::info(method () { 42 })->invocants;
    # ('$self')
    my $slurpy = Function::Parameters::info(fun (@) {})->slurpy;  # '@'
```

## DESCRIPTION

`"Function::Parameters::info"` returns objects of this class to describe parameter lists of functions. See below for "Parameter Objects".  The following methods are available:

*$info-\>invocants*

Returns a list of parameter objects for the variables into which initial arguments are `"shift"`ed automatically (or a count in scalar context). This will usually return `"()"` for normal functions and `"('$self')"` for methods.

*$info-\>positional\_required*

Returns a list of parameter objects for the required positional parameters (or a count in scalar context).

*$info-\>positional\_optional*

Returns a list of parameter objects for the optional positional parameters (or a count in scalar context).

*$info-\>named\_required*

Returns a list of parameter objects for the required named parameters (or a count in scalar context).

*$info-\>named\_optional*

Returns a list of parameter objects for the optional named parameters (or a count in scalar context).

*$info-\>slurpy*

Returns a parameter object for the final array or hash that gobbles up all remaining arguments, or `"undef"` if no such thing exists.

*$info-\>args\_min*

Returns the minimum number of arguments this function requires. This is computed as follows: Invocants and required positional parameters count 1 each. Optional parameters don't count. Required named parameters count 2 each (key + value). Slurpy parameters don't count either because they accept empty lists.

*$info-\>args\_max*

Returns the maximum number of arguments this function accepts. This is computed as follows: If there are any named or slurpy parameters, the result is `"Inf"`. Otherwise the result is the number of all invocants and positional parameters.

*$info-\>invocant*

Similar to "$info-\>invocants" above: Returns `"undef"` if the number of invocants is 0, a parameter object for the invocant if there is exactly 1, and throws an exception otherwise.

*Parameter Objects*

Many of the methods described above return parameter objects.  These objects have two methods: `"name"`, which returns the name of the parameter (as a plain string), and `"type"`, which returns the corresponding type constraint object (or undef if there was no type specified).

This should be invisible if you don't care about types because the objects also overload stringification to call `"name"`. That is, if you treat parameter objects like strings, they behave like strings (i.e. their names).

## SEE ALSO

Function::Parameters

## AUTHOR

Lukas Mai, `"<l.mai at web.de>"`

## COPYRIGHT & LICENSE

Copyright 2013, 2016 Lukas Mai.

This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.

See http://dev.perl.org/licenses/ for more information.