I am confused by how PHP call method in parent-children hierarchy. Here is the code
class A { private function foo() { echo "A!"; } public function test() { $this->foo(); } } class C extends A { public function foo() { echo 'C!'; } } $c = new C(); $c->test();
The output is A!
consider another example, but only change the foo() method visibility in class A to be public.
class A { public function foo() { echo "A!"; } public function test() { $this->foo(); } } class C extends A { public function foo() { echo 'C!'; } } $c = new C(); $c->test();
This output is C!
Any explanation is welcome.
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Answer
Rule: private
and final
methods on an object will always be called directly, without consulting the override table.
This rule is baked into the engine:
/* Check if this calls a known method on $this */ if (opline->op1_type == IS_UNUSED && opline->op2_type == IS_CONST && CG(active_class_entry) && zend_is_scope_known()) { zend_string *lcname = Z_STR_P(CT_CONSTANT(opline->op2) + 1); fbc = zend_hash_find_ptr(&CG(active_class_entry)->function_table, lcname); /* We only know the exact method that is being called if it is either private or final. * Otherwise an overriding method in a child class may be called. */ if (fbc && !(fbc->common.fn_flags & (ZEND_ACC_PRIVATE|ZEND_ACC_FINAL))) { fbc = NULL; } }
“Why”, you ask? The answer is: because that’s how it works. In language design, this is called “name hiding”, and it’s up to the language to specify how name hiding works. Take C++ for example. It has well-defined, and complex name hiding rules. PHP has its own rules. They’re different from C++. But they’re unique to PHP. This is just something you have to memorize about the language.
I admit the docs could better spell this out, however.