Boolean

Ensure that variable has value that can be treated as bool value. Variable is validated and converted to bool value on success.

Correct:

assure($x = true, 'boolean');  // $x => true
assure($x = false, 'boolean');  // $x => false
assure($x = 1, 'boolean');  // $x => true
assure($x = 0, 'boolean');  // $x => false
assure($x = 'true', 'boolean');  // $x => true
assure($x = 'false', 'boolean');  // $x => false
assure($x = 'TRUE', 'boolean');  // $x => true
assure($x = 'FALSE', 'boolean');  // $x => false
assure($x = 'True', 'boolean');  // $x => true
assure($x = 'False', 'boolean');  // $x => false
assure($x = 'on', 'boolean');  // $x => true
assure($x = 'off', 'boolean');  // $x => false
assure($x = 'ON', 'boolean');  // $x => true
assure($x = 'OFF', 'boolean');  // $x => false
assure($x = 'YES', 'boolean');  // $x => true
assure($x = 'NO', 'boolean');  // $x => false
assure($x = 'yes', 'boolean');  // $x => true
assure($x = 'no', 'boolean');  // $x => false
assure($x = 'falsE', 'boolean');  // $x => true
assure($x = 'truE', 'boolean');  // $x => false

Incorect:

assure($x = '2', 'boolean');
assure($x = 2, 'boolean');
assure($x = new \stdClass, 'boolean');
assure($x = 'a', 'boolean');
assure($x = 'one', 'boolean');

All above method calls will throw \InvalidArgumentException