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Module Version: 1.002001   Source  

NAME ^

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

SYNOPSIS ^

 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);

STATUS ^

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

DESCRIPTION ^

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) = $deposit_monies_check->(@_);
    
    ...;
 }

Not quite as neat, but not awful either.

There's a shortcut reducing it to one step:

 use Type::Params qw( validate validate_named );
 
 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.

COOKBOOK ^

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;
      $self->_run;
   }

Of course, some people like to use shift for the invocant:

   sub dump
   {
      my $self = shift;
      
      state $check = compile( Int );
      my ($limit) = $check->(@_);
      
      local $Data::Dumper::Maxdepth = $limit;
      print Data::Dumper::Dumper($self);
   }

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.

Having a slurpy parameter will slightly slow down your checks.

Named Parameters

You can use compile_named to accept a hash of named parameters

   use Type::Params qw(compile_named);
   use Types::Standard qw( slurpy Dict Ref Optional Int );
   
   sub dump
   {
      state $check = compile_named(
         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 (hashref)
   dump(  var => $foo, limit => 1  );    # ok (hash)
   dump(  var => $foo  );                # ok (no optional parameter)
   dump(  limit => 1  );                 # dies

Prior to Type::Tiny 1.002000, the recommendation was to use a slurpy Dict. This still works, though the error messages you get might not be quite so nice, and you don't get the automatic detection of hash versus hashref in the input @_. Oh, and it's usually slower.

   use Type::Params qw(compile);
   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 (hash)
   dump(  var => $foo  );                # ok (no optional parameter)
   dump(  limit => 1  );                 # dies

Mixed Positional and Named Parameters

For this, you can still use the slurpy Dict hack...

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

Coercions

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 prevent 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 $_.

Having any coercions will slightly slow down your checks.

Alternatives

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.

The magic global ${^TYPE_PARAMS_MULTISIG} is set to the index of the first signature which 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 ],
      compile_named( needle => Value, haystack => Ref ),
   );

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->(@_);
      
      for (${^TYPE_PARAMS_MULTISIG) {
         return $haystack->[$needle] if $_ == 0;
         return $haystack->{$needle} if $_ == 1;
         return $haystack->$needle   if $_ == 2;
      }
   }
   
   get_from(0, \@array);      # returns $array[0]
   get_from('foo', \%hash);   # returns $hash{foo}
   get_from('foo', $obj);     # returns $obj->foo

Defaults

Type::Params does not currently offer a built-in way to set defaults for a parameter. Setting defaults manually is not especially difficult.

   sub print_coloured {
      state $check = compile( Str, Optional[Str] );
      
      my ($text, $colour) = $check->(@_);
      $colour //= "black";
      
      ...;
   }

I occasionally get requests for this to work:

   sub print_coloured {
      state $check = compile( Str, Default[Str, "black"] );
      
      my ($text, $colour) = $check->(@_);
      
      ...;
   }

But honestly, I don't find that any clearer.

COMPARISON WITH 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.

COMPARISON WITH PARAMS::VALIDATIONCOMPILER ^

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

BUGS ^

Please report any bugs to http://rt.cpan.org/Dist/Display.html?Queue=Type-Tiny.

SEE ALSO ^

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

AUTHOR ^

Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE ^

This software is copyright (c) 2013-2014, 2017 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.

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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