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constant::boolean - Define TRUE and FALSE constants.


  use constant::boolean;

  use File::Spec;

  sub is_package_exist {
    my ($package) = @_;
    return FALSE unless defined $package;
    foreach my $inc (@INC) {
        my $filename = File::Spec->catfile(
            split( /\//, $inc ), split( /\::/, $package )
        ) . '.pm';
        return TRUE if -f $filename;
    return FALSE;

  no constant::boolean;


Defines TRUE and FALSE constants in caller's namespace. You could use simple values like empty string or zero for false, or any non-empty and non-zero string value as true, but the TRUE and FALSE constants are more descriptive.

It is virtually the same as:

  # double "not" operator is used for converting scalar to boolean value
  use constant TRUE => !! 1;
  use constant FALSE => !! '';

The constants exported by constant::boolean are not reported by Test::Pod::Coverage, so it is more convenient to use this module than to define TRUE and FALSE constants by yourself.

The constants can be removed from class API with no constant::boolean pragma or some universal tool like namespace::clean.


If you find the bug or want to implement new features, please report it at


Piotr Roszatycki <>


Copyright 2008, 2009 by Piotr Roszatycki <>.

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