Question

According to my tests on http://3v4l.org/ZCJWA following example (For PHP 5.3.10 – 5.4.6):

<?php
namespace Foo;
define('Foo\\true', false);
define('Foo\\false', true);

var_dump(
    true,
    false,
    1 === 1,
    1 === 0
);

will return:

bool(false)
bool(false)
bool(true)
bool(false)

Why can you overwrite true with false but not false with true?

Answer 1

After your 1st define, true is now defined to be false, so Foo\\false gets set to false.

To get it working as expected, you should should be setting Foo\\true and Foo\\false to the global space values of true and false respectively:

define('Foo\\true', \false);
define('Foo\\false', \true);