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<?php class Super { public $child; function setChild(Child $child){ echo "setting child to super\n"; $this->child = $child; if($child->getSuper() !== $this) $child->setSuper($this); } function getChild(){ return $this->child; } } class Child { public $super; function setSuper(Super $super){ echo "setting super to child\n"; $this->super = $super; if($super->getChild() !== $this) $this->super->setChild($this); } function getSuper(){ return $this->super; } } $super = new Super; $child = new Child; $super->setChild($child); var_dump($super); $super = new Super; $child = new Child; $child->setSuper($super); var_dump($super);
Output for 5.4.9 - 5.4.45, 5.5.24 - 5.5.35, 5.6.8 - 5.6.28, 7.0.0 - 7.0.20, 7.1.0 - 7.1.20, 7.2.0 - 7.2.33, 7.3.16 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.29, 8.2.0 - 8.2.21, 8.3.0 - 8.3.9
setting child to super setting super to child object(Super)#1 (1) { ["child"]=> object(Child)#2 (1) { ["super"]=> *RECURSION* } } setting super to child setting child to super object(Super)#3 (1) { ["child"]=> object(Child)#4 (1) { ["super"]=> *RECURSION* } }

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159.56 ms | 405 KiB | 226 Q