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Manual Reference Pages  -  TYPE::PARAMS (3)

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Type::Params - Params::Validate-like parameter validation using Type::Tiny type constraints and coercions



 use v5.10;
 use strict;
 use warnings;

 use Type::Params qw( compile );
 use Types::Standard qw( slurpy Str ArrayRef Num );
 sub deposit_monies
    state $check = compile( Str, Str, slurpy ArrayRef[Num] );
    my ($sort_code, $account_number, $monies) = $check->(@_);
    my $account = Local::BankAccount->new($sort_code, $account_number);
    $account->deposit($_) for @$monies;

 deposit_monies("12-34-56", "11223344", 1.2, 3, 99.99);


This module is covered by the Type-Tiny stability policy.


Type::Params uses Type::Tiny constraints to validate the parameters to a sub. It takes the slightly unorthodox approach of separating validation into two stages:
1. Compiling the parameter specification into a coderef; then
2. Using the coderef to validate parameters.
The first stage is slow (it might take a couple of milliseconds), but you only need to do it the first time the sub is called. The second stage is fast; according to my benchmarks faster even than the XS version of Params::Validate.

If you’re using a modern version of Perl, you can use the state keyword which was a feature added to Perl in 5.10. If you’re stuck on Perl 5.8, the example from the SYNOPSIS could be rewritten as:

 my $deposit_monies_check;
 sub deposit_monies
    $deposit_monies_check ||= compile( Str, Str, slurpy ArrayRef[Num] );
    my ($sort_code, $account_number, $monies) = $check->(@_);

Not quite as neat, but not awful either.

There’s a shortcut reducing it to one step:

 use Type::Params qw( validate );

 sub deposit_monies
    my ($sort_code, $account_number, $monies) =
       validate( \@_, Str, Str, slurpy ArrayRef[Num] );

Type::Params has a few tricks up its sleeve to make sure performance doesn’t suffer too much with the shortcut, but it’s never going to be as fast as the two stage compile/execute.


    Positional Parameters

   sub nth_root
      state $check = compile( Num, Num );
      my ($x, $n) = $check->(@_);
      return $x ** (1 / $n);

    Method Calls

Type::Params exports an additional keyword Invocant on request. This is a type constraint accepting blessed objects and also class names.

   use Types::Standard qw( ClassName Object Str Int );
   use Type::Params qw( compile Invocant );
   # a class method
   sub new_from_json
      state $check = compile( ClassName, Str );
      my ($class, $json) = $check->(@_);
      $class->new( from_json($json) );
   # an object method
   sub dump
      state $check = compile( Object, Int );
      my ($self, $limit) = $check->(@_);
      local $Data::Dumper::Maxdepth = $limit;
      print Data::Dumper::Dumper($self);
   # can be called as either and object or class method
   sub run
      state $check = compile( Invocant );
      my ($proto) = $check->(@_);
      my $self = ref($proto) ? $proto : $default_instance;

    Optional Parameters

   use Types::Standard qw( Object Optional Int );
   sub dump
      state $check = compile( Object, Optional[Int] );
      my ($self, $limit) = $check->(@_);
      $limit //= 0;
      local $Data::Dumper::Maxdepth = $limit;
      print Data::Dumper::Dumper($self);
   $obj->dump(1);      # ok
   $obj->dump();       # ok
   $obj->dump(undef);  # dies

    Slurpy Parameters

   use Types::Standard qw( slurpy ClassName HashRef );
   sub new
      state $check = compile( ClassName, slurpy HashRef );
      my ($class, $ref) = $check->(@_);
      bless $ref => $class;
   __PACKAGE__->new(foo => 1, bar => 2);

The following types from Types::Standard can be made slurpy: ArrayRef, Tuple, HashRef, Map, Dict. Hash-like types will die if an odd number of elements are slurped in.

A check may only have one slurpy parameter, and it must be the last parameter.

    Named Parameters

Just use a slurpy Dict:

   use Types::Standard qw( slurpy Dict Ref Optional Int );
   sub dump
      state $check = compile(
         slurpy Dict[
            var    => Ref,
            limit  => Optional[Int],
      my ($arg) = $check->(@_);
      local $Data::Dumper::Maxdepth = $arg->{limit};
      print Data::Dumper::Dumper($arg->{var});
   dump(var => $foo, limit => 1);   # ok
   dump(var => $foo);               # ok
   dump(limit => 1);                # dies

    Mixed Positional and Named Parameters

   use Types::Standard qw( slurpy Dict Ref Optional Int );
   sub my_print
      state $check = compile(
         slurpy Dict[
            colour => Optional[Str],
            size   => Optional[Int],
      my ($string, $arg) = $check->(@_);
   my_print("Hello World", colour => "blue");


Coercions will automatically be applied for all type constraints that have a coercion associated.

   use Type::Utils;
   use Types::Standard qw( Int Num );
   my $RoundedInt = declare as Int;
   coerce $RoundedInt, from Num, q{ int($_) };
   sub set_age
      state $check = compile( Object, $RoundedInt );
      my ($self, $age) = $check->(@_);
      $self->{age} = $age;
   $obj->set_age(32.5);   # ok; coerced to "32".

Coercions carry over into structured types such as ArrayRef automatically:

   sub delete_articles
      state $check = compile( Object, slurpy ArrayRef[$RoundedInt] );
      my ($db, $articles) = $check->(@_);
      $db->select_article($_)->delete for @$articles;
   # delete articles 1, 2 and 3
   delete_articles($my_db, 1.1, 2.2, 3.3);

If type Foo has coercions from Str and ArrayRef and you want to <B>preventB> coercion, then use:

   state $check = compile( Foo->no_coercions );

Or if you just want to prevent coercion from Str, use:

   state $check = compile( Foo->minus_coercions(Str) );

Or maybe add an extra coercion:

   state $check = compile(
      Foo->plus_coercions(Int, q{ Foo->new_from_number($_) }),

Note that the coercion is specified as a string of Perl code. This is usually the fastest way to do it, but a coderef is also accepted. Either way, the value to be coerced is $_.


Type::Params can export a multisig function that compiles multiple alternative signatures into one, and uses the first one that works:

   state $check = multisig(
      [ Int, ArrayRef ],
      [ HashRef, Num ],
      [ CodeRef ],
   my ($int, $arrayref) = $check->( 1, [] );
   my ($hashref, $num)  = $check->( {}, 1.1 );
   my ($code)           = $check->( sub { 1 } );
   $check->( sub { 1 }, 1.1 );  # throws an exception

Coercions, slurpy parameters, etc still work.

There’s currently no indication of which of the multiple signatures succeeded.

The present implementation involves compiling each signature independently, and trying them each (in their given order!) in an eval block. The only slightly intelligent part is that it checks if scalar(@_) fits into the signature properly (taking into account optional and slurpy parameters), and skips evals which couldn’t possibly succeed.

It’s also possible to list coderefs as alternatives in multisig:

   state $check = multisig(
      [ Int, ArrayRef ],
      sub { ... },
      [ HashRef, Num ],
      [ CodeRef ],

The coderef is expected to die if that alternative should be abandoned (and the next alternative tried), or return the list of accepted parameters. Here’s a full example:

   sub get_from {
      state $check = multisig(
         [ Int, ArrayRef ],
         [ Str, HashRef ],
         sub {
            my ($meth, $obj);
            die unless is_Object($obj);
            die unless $obj->can($meth);
            return ($meth, $obj);
      my ($needle, $haystack) = $check->(@_);
      is_HashRef($haystack)  ? $haystack->{$needle} :
      is_ArrayRef($haystack) ? $haystack->[$needle] :
      is_Object($haystack)   ? $haystack->$needle   :
   get_from(0, \@array);      # returns $array[0]
   get_from(foo, \%hash);   # returns $hash{foo}
   get_from(foo, $obj);     # returns $obj->foo


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.
o 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.
o Type::Params is mostly geared towards positional parameters, while Params::Validate seems to be primarily aimed at named parameters. (Though either works for either.) Params::Validate doesn’t appear to have a particularly natural way of validating a mix of positional and named parameters.
o Type::Utils allows you to coerce parameters. For example, if you expect a Path::Tiny object, you could coerce it from a string.
o Params::Validate allows you to supply defaults for missing parameters; Type::Params does not, but you may be able to use coercion from Undef.
o 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.
o 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.


Please report any bugs to <>.


Type::Tiny, Type::Coercion, Types::Standard.


Toby Inkster <>.


This software is copyright (c) 2013-2014 by Toby Inkster.

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


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perl v5.20.3 TYPE::PARAMS (3) 2014-10-25

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