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<?php class test implements JsonSerializable { public $a = 2; public function JsonSerialize() { return array('b' => 2, 'test'=>$this); } } var_dump(json_encode(new test())); var_dump(json_last_error_msg());
Output for 8.1.0 - 8.1.27, 8.2.0 - 8.2.17, 8.3.0 - 8.3.4
Deprecated: Return type of test::JsonSerialize() should either be compatible with JsonSerializable::jsonSerialize(): mixed, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /in/o6p5G on line 5 bool(false) string(18) "Recursion detected"
Output for 5.5.0 - 5.5.38, 5.6.0 - 5.6.28, 7.0.0 - 7.0.20, 7.1.0 - 7.1.33, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30
bool(false) string(18) "Recursion detected"
Output for 5.4.4 - 5.4.45
Warning: json_encode(): recursion detected in /in/o6p5G on line 10 string(34) "{"b":2,"test":{"b":2,"test":null}}" Fatal error: Call to undefined function json_last_error_msg() in /in/o6p5G on line 11
Process exited with code 255.
Output for 5.4.0 - 5.4.3

Process exited with code 139.
Output for 5.0.5, 5.1.0 - 5.1.6, 5.2.0 - 5.2.17, 5.3.0 - 5.3.29
Fatal error: Interface 'JsonSerializable' not found in /in/o6p5G on line 3
Process exited with code 255.
Output for 5.0.0 - 5.0.4
Fatal error: Class 'JsonSerializable' not found in /in/o6p5G on line 3
Process exited with code 255.
Output for 4.4.2 - 4.4.9
Parse error: syntax error, unexpected T_STRING, expecting '{' in /in/o6p5G on line 3
Process exited with code 255.
Output for 4.3.0 - 4.3.1, 4.3.5 - 4.3.11, 4.4.0 - 4.4.1
Parse error: parse error, unexpected T_STRING, expecting '{' in /in/o6p5G on line 3
Process exited with code 255.
Output for 4.3.2 - 4.3.4
Parse error: parse error, expecting `'{'' in /in/o6p5G on line 3
Process exited with code 255.

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