/* ArrayAccess接口的继承实现 */
REGISTER_SPL_IMPLEMENTS(CachingIterator, ArrayAccess);
 
//    ext/spl/spl_functions.h 41行
#define REGISTER_SPL_IMPLEMENTS(class_name, interface_name) \
	zend_class_implements(spl_ce_ ## class_name TSRMLS_CC, 1, spl_ce_ ## interface_name);
 
//	zend/zend_API.c 2218行
ZEND_API void zend_class_implements(zend_class_entry *class_entry TSRMLS_DC, int num_interfaces, ...) /* {{{ */
{
	zend_class_entry *interface_entry;
	va_list interface_list;
	va_start(interface_list, num_interfaces);
 
	while (num_interfaces--) {
		interface_entry = va_arg(interface_list, zend_class_entry *);
		zend_do_implement_interface(class_entry, interface_entry TSRMLS_CC);
	}
 
	va_end(interface_list);
}
/* }}} */
 
 
 
//	zend/zend_complie.c 2887行
ZEND_API void zend_do_implement_interface(zend_class_entry *ce, zend_class_entry *iface TSRMLS_DC) /* {{{ */
{
	zend_uint i, ignore = 0;
	zend_uint current_iface_num = ce->num_interfaces;
	zend_uint parent_iface_num  = ce->parent ? ce->parent->num_interfaces : 0;
 
	for (i = 0; i < ce->num_interfaces; i++) {
		if (ce->interfaces[i] == NULL) {
			memmove(ce->interfaces + i, ce->interfaces + i + 1, sizeof(zend_class_entry*) * (--ce->num_interfaces - i));
			i--;
		} else if (ce->interfaces[i] == iface) {	/* 已存在此接口 */
			if (i < parent_iface_num) {
				ignore = 1;
			} else {
				zend_error(E_COMPILE_ERROR, "Class %s cannot implement previously implemented interface %s", ce->name, iface->name);
			}
		}
	}
	if (!ignore) {
		if (ce->num_interfaces >= current_iface_num) {
			if (ce->type == ZEND_INTERNAL_CLASS) {
				ce->interfaces = (zend_class_entry **) realloc(ce->interfaces, sizeof(zend_class_entry *) * (++current_iface_num));
			} else {
				ce->interfaces = (zend_class_entry **) erealloc(ce->interfaces, sizeof(zend_class_entry *) * (++current_iface_num));
			}
		}
		ce->interfaces[ce->num_interfaces++] = iface;	//	接口数加1，将接口加入接口列表中
 
		/* 合并接口中的常量列表和方法列表 */
		zend_hash_merge_ex(&ce->constants_table, &iface->constants_table, (copy_ctor_func_t) zval_add_ref, sizeof(zval *), (merge_checker_func_t) do_inherit_constant_check, iface);
		zend_hash_merge_ex(&ce->function_table, &iface->function_table, (copy_ctor_func_t) do_inherit_method, sizeof(zend_function), (merge_checker_func_t) do_inherit_method_check, ce);
 
		do_implement_interface(ce, iface TSRMLS_CC);
		zend_do_inherit_interfaces(ce, iface TSRMLS_CC);
	}
}

<?php
interface FooInterface {
	public function method1();
}
 
class Base implements FooInterface {
	public function method1() {
		echo 'ss';
	}
}
 
class Foo extends Base implements FooInterface {
 
}
 
$foo = new Foo();
$foo->method1();