Provided by: libtype-tiny-perl_1.000005-1_all bug


       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


   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

          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 $_.

       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.

       ·   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.

       ·   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.

       ·   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.


       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.