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run code in 300+ PHP versions simultaneously
<?php interface Thing { } class Foo implements Thing { } class Bar extends Foo { } class Zulu { } var_dump( is_subclass_of('Foo', 'Thing'), is_a('Foo', 'Thing', TRUE), is_subclass_of('Bar', 'Thing'), is_a('Bar', 'Thing', TRUE), is_subclass_of('Zulu', 'Thing'), is_a('Zulu', 'Thing', TRUE), is_subclass_of('Foo', 'Foo'), is_a('Foo', 'Foo', TRUE) );

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