Type::Tiny::Manual::Params

(source, CPAN)

#NAME

Type::Tiny::Manual::Params - advanced information on Type::Params

#MANUAL

To get started with Type::Params, please read Type::Tiny::Manual::UsingWithMoo which will cover a lot of the basics, even if you're not using Moo.

#`multiple`

The multiple option allows you to specify multiple ways of calling a sub.

sub repeat_string {
  state $check = signature(
    multiple => [
      { positional => [ Str, Int ] },
      { named => [ string => Str, count => Int ], named_to_list => 1 },
    ],
  );
  
  my ( $string, $count ) = $check->( @_ );
  return $string x $count;
}

repeat_string(            "Hello",          42  );    # works
repeat_string(  string => "Hello", count => 42  );    # works
repeat_string({ string => "Hello", count => 42 });    # works
repeat_string( qr/hiya/ );                            # dies

It combines multiple checks and tries each until one works.

#`signature_for`

signature_for turns signature inside out.

Instead of this:

sub foobar {
  state $check = signature( positional => [ Int, Str ] );
  my ( $foo, $bar ) = $check->( @_ );
  ...;
}

You do this:

signature_for foobar => (
  positional => [ Int, Str ],
);

sub foobar {
  my ( $foo, $bar ) = @_;
  ...;
}

Or in Perl 5.20+, you can even do this:

signature_for foobar => (
  positional => [ Int, Str ],
);

sub foobar ( $foo, $bar ) {
  ...;
}

#Functions versus Methods

For subs which are intended to be called as functions:

signature( method => 0, ... );
signature( ... );                       # this is the default anyway

For subs which are intended to be called as methods on a blessed object:

signature( method => Object, ... );

And for subs which are intended to be called as methods on a class:

signature( method => ClassName, ... );
signature( method => Str, ... );        # less readable, but faster check!

The following is also allowed, which indicates that the sub is intended to be called as a method, but you don't want to do type checks on the invocant:

signature( method => 1, ... );

#Mixed Named and Positional Parameters

The head and tail options allow required positional parameters at the start or end of a named parameter list:

state $check = signature(
  head  => [ Int ],
  named => [
    foo => Int,
    bar => Optional[Int],
    baz => Optional[Int],
  ],
);

$check->( 42, foo => 21 );                 # ok
$check->( 42, foo => 21, bar  => 84 );     # ok
$check->( 42, foo => 21, bar  => 10.5 );   # not ok
$check->( 42, foo => 21, quux => 84 );     # not ok

#Proper Signatures

Don't you wish your subs could look like this?

sub set_name ( Object $self, Str $name ) {
  $self->{name} = $name;
}

Well; here are a few solutions for sub signatures that work with Type::Tiny...

#Zydeco

Zydeco is a Perl OO syntax toolkit with Type::Tiny support baked in throughout.

package MyApp {
  use Zydeco;
  
  class Person {
    has name ( type => Str );
    
    method rename ( Str $new_name ) {
      printf( "%s will now be called %s\n", $self->name, $new_name );
      $self->name( $new_name );
    }
    
    coerce from Str via {
      $class->new( name => $_ )
    }
  }
  
  class Company {
    has owner ( type => 'Person' );
  }
}

my $acme = MyApp->new_company( owner => "Robert" );
$acme->owner->rename( "Bob" );

#Kavorka

Kavorka is a sub signatures implementation written to natively use Type::Utils' dwim_type for type constraints, and take advantage of Type::Tiny's features such as inlining, and coercions.

method set_name ( Str $name ) {
  $self->{name} = $name;
}

Kavorka's signatures provide a lot more flexibility, and slightly more speed than Type::Params. (The speed comes from inlining almost all type checks into the body of the sub being declared.)

Kavorka also includes support for type checking of the returned value.

Kavorka can also be used as part of Moops, a larger framework for object oriented programming in Perl.

#Function::Parameters

Function::Parameters offers support for Type::Tiny and MooseX::Types.

use Types::Standard qw( Str );
use Function::Parameters;

method set_name ( Str $name ) {
    $self->{name} = $name;
}

#Attribute::Contract

Both Kavorka and Function::Parameters require a relatively recent version of Perl. Attribute::Contract supports older versions by using a lot less magic.

You want Attribute::Contract 0.03 or above.

use Attribute::Contract -types => [qw/Object Str/];

sub set_name :ContractRequires(Object, Str) {
    my ($self, $name) = @_;
    $self->{name} = $name;
}

Attribute::Contract also includes support for type checking of the returned value.

#Type::Params versus X

#Params::Validate

Type::Params is not really a drop-in replacement for Params::Validate; the API differs far too much to claim that. Yet it performs a similar task, so it makes sense to compare them.

Type::Params will tend to be faster if you've got a sub which is called repeatedly, but may be a little slower than Params::Validate for subs that are only called a few times. This is because it does a bunch of work the first time your sub is called to make subsequent calls a lot faster.
Params::Validate doesn't appear to have a particularly natural way of validating a mix of positional and named parameters.
Type::Utils allows you to coerce parameters. For example, if you expect a Path::Tiny object, you could coerce it from a string.
If you are primarily writing object-oriented code, using Moose or similar, and you are using Type::Tiny type constraints for your attributes, then using Type::Params allows you to use the same constraints for method calls.
Type::Params comes bundled with Types::Standard, which provides a much richer vocabulary of types than the type validation constants that come with Params::Validate. For example, Types::Standard provides constraints like ArrayRef[Int] (an arrayref of integers), while the closest from Params::Validate is ARRAYREF, which you'd need to supplement with additional callbacks if you wanted to check that the arrayref contained integers.

Whatsmore, Type::Params doesn't just work with Types::Standard, but also any other Type::Tiny type constraints.

#Params::ValidationCompiler

Params::ValidationCompiler does basically the same thing as Type::Params.

Params::ValidationCompiler and Type::Params are likely to perform fairly similarly. In most cases, recent versions of Type::Params seem to be slightly faster, but except in very trivial cases, you're unlikely to notice the speed difference. Speed probably shouldn't be a factor when choosing between them.

Type::Params's syntax is more compact:

state $check = signature(
  pos => [
    Object,
    Optional[Int],
    Slurpy[ArrayRef],
  ],
);

Versus:

state $check = validation_for(
   params => [
      { type => Object },
      { type => Int,      optional => 1 },
      { type => ArrayRef, slurpy => 1 },
   ],
);

Params::ValidationCompiler probably has slightly better exceptions.

#NEXT STEPS

Here's your next step:

Type::Tiny::Manual::NonOO

Type::Tiny in non-object-oriented code.

#AUTHOR

Toby Inkster <tobyink@cpan.org>.

#COPYRIGHT AND LICENCE

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.

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