A brief discussion on PHP source code twenty-seven: PHP's identification of construction methods

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Talking about PHP source code twenty-seven: PHP's identification of constructor methods
As we all know, due to historical reasons, PHP used to use the class name as the constructor, and the new constructor __construct was introduced in PHP5. For backward compatibility, if PHP 5 cannot find a __construct() function in a class, it will try to find an old-style constructor, which is a function with the same name as the class. Therefore, the only situation where compatibility issues will arise is if the class already has a method named __construct(), but it is not a constructor.
There is the following piece of code

<?php
class Foo {     
public function Foo() {     
}     
private function __construct() {     
}
} 
new Foo();
die();

At this time, the output is:

Fatal error: Call to private Foo::__construct() from invalid context

At this time, The constructor recognized by PHP is __construct. Because it is private, an error occurs when calling externally.

Okay, let’s find out the reason from the C source code of PHP.

Start by directly looking for the definition of the class in the extension class of spl:

 spl_iterators.c 3228行 REGISTER_SPL_STD_CLASS_EX(IteratorIterator, spl_dual_it_new, spl_funcs_IteratorIterator);///spl_functions.h 31行#define REGISTER_SPL_STD_CLASS_EX(class_name, obj_ctor, funcs) \
spl_register_std_class(&spl_ce_ ## class_name, # class_name, obj_ctor, funcs TSRMLS_CC);//spl_functions.c 41行PHPAPI void spl_register_std_class(zend_class_entry ** ppce, char * class_name, void * obj_ctor, const zend_function_entry * function_list TSRMLS_DC) //spl_functions.c 2235行ZEND_API zend_class_entry *zend_register_internal_class(zend_class_entry *orig_class_entry TSRMLS_DC) /* {{{ *///调用do_register_internal_class函数 //zend_API.c 2169行static zend_class_entry *do_register_internal_class(zend_class_entry *orig_class_entry, zend_uint ce_flags TSRMLS_DC) /* {{{ *///调用zend_register_functions(class_entry, class_entry->builtin_functions, &class_entry->function_table, MODULE_PERSISTENT TSRMLS_CC); //zend_API.c 1795行/* Look for ctor, dtor, clone
* If it's an old-style constructor, store it only if we don't have
* a constructor already.
*/if ((fname_len == class_name_len) && !memcmp(lowercase_name, lc_class_name, class_name_len+1) && !ctor) {
ctor = reg_function;} else if ((fname_len == sizeof(ZEND_CONSTRUCTOR_FUNC_NAME)-1) && !memcmp(lowercase_name, ZEND_CONSTRUCTOR_FUNC_NAME, sizeof(ZEND_CONSTRUCTOR_FUNC_NAME))) {
ctor = reg_function;}  
scope->constructor = ctor;//在1961行 确认构造函数

The above code is the php5.3.0 version
From the above tracking process, when the program registers all functions, If __construct (i.e. ZEND_CONSTRUCTOR_FUNC_NAME) exists, the constructor of class_name (class name) will be overwritten so that it exists as a regular member function. The code is as follows:

<?php
class Foo {     
public function Foo() {
        echo &#39;Foo&#39;;
    }     public function __construct() {
        echo &#39;__construct&#39;;
    }} 
    $foo = new Foo();
    $foo->Foo();

For the error reported in the previous example, we can

ZEND_API union _zend_function *zend_std_get_constructor(zval *object TSRMLS_DC )
Find the source.

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