JSON::Types(3) variable type utility for JSON encoding


# Export type functions by default
use JSON;
use JSON::Types;

print encode_json({
number => number "123",
string => string 123,
bool => bool "True value",
# => {"number":123,"string":"123","bool":true}

# Non export interface
use JSON::Types ();

print encode_json({
number => JSON::Types::number "123",
string => JSON::Types::string 123,
bool => JSON::Types::bool "True value",


The type mappings between JSON and Perl is annoying things. For example,

    use JSON;
    my $number = 123;
    warn "[DEBUG] number:$number\n" if $ENV{DEBUG};
    print encode_json([ $number ]);

Output of this code depends on whether DEBUG environment is set or not. If set, result is "[123]". If not to set, result is "["123"]". This is normal behaviour on Perl though, it sometimes causes unexpected JSON results.

There is a solution about this:

    print encode_json([ $number + 0 ]);

This code always outputs "[123]". But the code is a bit ugly and not readable at all.

This module provides some functions to fix this variable types issue:

    number $foo;  # is always number
    string $foo;  # is always string
    bool   $foo;  # is always bool

You can fix above code by using this module like this:

    use JSON;
    use JSON::Types;
    my $number = 123;
    warn "[DEBUG] number:$number\n" if $ENV{DEBUG};
    print encode_json([ number $number ]);


There is three functions and all functions is exported by default.

If you don't want this exported functions, pass empty list to use line:

    use JSON::Types ();

You should specify full function name when this case, like "JSON::Types::number $foo" or etc.





string(undef), number(undef) returns undef, bool(undef) returns false.

Passing undefined variable to string and number function is returns undef. If you doesn't prefer this, have to treat this like following:

    number $undef_possible_value // 0

This code returns 0 if variable is undef.


Passing not numeric variable to number function is returns 0, but a warning will be occurred.


Daisuke Murase <[email protected]>


Copyright (c) 2012 Daisuke Murase. All rights reserved.

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

The full text of the license can be found in the LICENSE file included with this module.