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);

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) = $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.

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;
       }

  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 $check = compile(
             Str,
             slurpy Dict[
                colour => Optional[Str],
                size   => Optional[Int],
             ],
          );
          my ($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 $_.

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

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

AUTHOR
    Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE
    This software is copyright (c) 2013 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.

