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JSON::Types - 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 <>


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.