Type::Params(3)

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.

•   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.

•   Params::Validate allows you to supply defaults for missing parameters; Type::Params does not, but you may be able to use coercion from Undef.

•   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.

COMPARISON WITH 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 = compile(Object, Optional[Int], slurpy ArrayRef);

    Versus:

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

•   Params::ValidationCompiler offers defaults.

•   Params::ValidationCompiler probably has slightly better exceptions.

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.