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run code in 300+ PHP versions simultaneously
<?php // Everything you enter here will be executed by our servers. Try it! class A { public $b; public function A(B $b = null){ if(is_null($b)) $b = new B(); $this->b = $b; } } class B { public $a; public function B(A $a = null) { if(is_null($a)) $a = new A(); $this->a = $a; } } var_dump(new A(new B(new A())));
Output for 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
object(A)#1 (1) { ["b"]=> NULL }
Output for 7.1.0 - 7.1.33, 7.2.0 - 7.2.6, 7.2.8 - 7.2.33, 7.3.0 - 7.3.31, 7.4.0 - 7.4.25, 7.4.27 - 7.4.33
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; A has a deprecated constructor in /in/kBkhL on line 4 Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; B has a deprecated constructor in /in/kBkhL on line 14 Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 4194304 bytes) in /in/kBkhL on line 8
Process exited with code 255.
Output for 7.4.26
Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 8388608 bytes) in /in/kBkhL on line 8
Process exited with code 255.
Output for 7.3.32 - 7.3.33
Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 8388608 bytes) in /in/kBkhL on line 8 mmap() failed: [12] Cannot allocate memory
Process exited with code 255.
Output for 7.2.7

Process exited with code 137.
Output for 7.0.0 - 7.0.33
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; A has a deprecated constructor in /in/kBkhL on line 4 Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; B has a deprecated constructor in /in/kBkhL on line 14 Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 4096 bytes) in /in/kBkhL on line 8
Process exited with code 255.
Output for 5.6.0 - 5.6.40
Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 130968 bytes) in /in/kBkhL on line 8
Process exited with code 255.
Output for 5.4.0 - 5.4.45, 5.5.0 - 5.5.38
Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 130968 bytes) in /in/kBkhL on line 18
Process exited with code 255.
Output for 5.3.0 - 5.3.29
Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 523800 bytes) in /in/kBkhL on line 8
Process exited with code 255.
Output for 5.1.0 - 5.1.6, 5.2.0 - 5.2.17

Process exited with code 139.
Output for 5.0.0 - 5.0.5
Fatal error: Argument 1 must not be null in /in/kBkhL on line 6
Process exited with code 255.
Output for 4.4.2 - 4.4.9
Parse error: syntax error, unexpected T_STRING, expecting T_OLD_FUNCTION or T_FUNCTION or T_VAR or '}' in /in/kBkhL on line 5
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 T_OLD_FUNCTION or T_FUNCTION or T_VAR or '}' in /in/kBkhL on line 5
Process exited with code 255.
Output for 4.3.2 - 4.3.4
Parse error: parse error, expecting `T_OLD_FUNCTION' or `T_FUNCTION' or `T_VAR' or `'}'' in /in/kBkhL on line 5
Process exited with code 255.
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