PHP源码阅读笔记二十八：类结构和继承
作为面向对象中一个非常关键也非常纠结的特性，我们需要了解一些
在PHP5中，从一开始就有了继承的概念，今天我们从PHP源码出发，了解他是怎么实现的。
在了解类的继承之前，我们需要知道类在PHP源码中是以哪种方式存储的。
找到zend/zend.h 418行：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 | struct _zend_class_entry { char type; char *name; /* 类名 */ zend_uint name_length; /* 类名字符串长度 */ struct _zend_class_entry *parent; /* 父类 */ int refcount; /* 引用计数 */ zend_bool constants_updated; zend_uint ce_flags; /* 类的访问控制 */ HashTable function_table; /* 类的成员函数 */ HashTable default_properties; /* 类的默认属性 */ HashTable properties_info; /* 类的属性信息 如访问控制等 */ HashTable default_static_members;/* 静态成员列表 */ HashTable *static_members; HashTable constants_table; /* 常量列表 */ const struct _zend_function_entry *builtin_functions; union _zend_function *constructor; /* 构造函数*/ union _zend_function *destructor; /* 析构函数*/ union _zend_function *clone; /* 克隆方法*/ /* 魔术方法 */ union _zend_function *__get; union _zend_function *__set; union _zend_function *__unset; union _zend_function *__isset; union _zend_function *__call; union _zend_function *__callstatic; union _zend_function *__tostring; union _zend_function *serialize_func; union _zend_function *unserialize_func; zend_class_iterator_funcs iterator_funcs; /* handlers */ zend_object_value (*create_object)(zend_class_entry *class_type TSRMLS_DC); zend_object_iterator *(*get_iterator)(zend_class_entry *ce, zval *object, int by_ref TSRMLS_DC); int (*interface_gets_implemented)(zend_class_entry *iface, zend_class_entry *class_type TSRMLS_DC); /* a class implements this interface */ union _zend_function *(*get_static_method)(zend_class_entry *ce, char* method, int method_len TSRMLS_DC); /* serializer callbacks */ int (*serialize)(zval *object, unsigned char **buffer, zend_uint *buf_len, zend_serialize_data *data TSRMLS_DC); int (*unserialize)(zval **object, zend_class_entry *ce, const unsigned char *buf, zend_uint buf_len, zend_unserialize_data *data TSRMLS_DC); zend_class_entry **interfaces; /* 类实现的接口 */ zend_uint num_interfaces; /* 类实现的接口数 */ /* 类所在文件信息 */ char *filename; zend_uint line_start; zend_uint line_end; char *doc_comment; zend_uint doc_comment_len; struct _zend_module_entry *module; }; |
从PHP自带的SPL中，我们可以看到有类的继承，从这里出发，可以找到我们所需要的实现过程
从手册中选择CachingIterator类作为切入点。
CachingIterator extends IteratorIterator implements OuterIterator , Traversable , Iterator , ArrayAccess , Countable
跟踪过程如下：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 | //在ext/spl/spl_iterators.c 3246行， REGISTER_SPL_SUB_CLASS_EX(CachingIterator, IteratorIterator, spl_dual_it_new, spl_funcs_CachingIterator); // ext/spl/spl_functions.h 34行 #define REGISTER_SPL_SUB_CLASS_EX(class_name, parent_class_name, obj_ctor, funcs) \ spl_register_sub_class(&spl_ce_ ## class_name, spl_ce_ ## parent_class_name, # class_name, obj_ctor, funcs TSRMLS_CC); // ext/spl/spl_functions.c 56行 PHPAPI void spl_register_sub_class(zend_class_entry ** ppce, zend_class_entry * parent_ce, char * class_name, void *obj_ctor, const zend_function_entry * function_list TSRMLS_DC) *ppce = zend_register_internal_class_ex(&ce, parent_ce, NULL TSRMLS_CC); // zend/zend_API.c 2196行 ZEND_API zend_class_entry *zend_register_internal_class_ex(zend_class_entry *class_entry, zend_class_entry *parent_ce, char *parent_name TSRMLS_DC) zend_do_inheritance(register_class, parent_ce TSRMLS_CC); // zend/zend_compile.c 2784行 ZEND_API void zend_do_inheritance(zend_class_entry *ce, zend_class_entry *parent_ce TSRMLS_DC) { /* 接口不能继承类 */ if ((ce->ce_flags & ZEND_ACC_INTERFACE) && !(parent_ce->ce_flags & ZEND_ACC_INTERFACE)) { zend_error(E_COMPILE_ERROR, "Interface %s may not inherit from class (%s)", ce->name, parent_ce->name); } /* final类不能继承 */ if (parent_ce->ce_flags & ZEND_ACC_FINAL_CLASS) { zend_error(E_COMPILE_ERROR, "Class %s may not inherit from final class (%s)", ce->name, parent_ce->name); } ce->parent = parent_ce; /* 拷贝序列化和反序列化回调函数 */ if (!ce->serialize) { ce->serialize = parent_ce->serialize; } if (!ce->unserialize) { ce->unserialize = parent_ce->unserialize; } /* 继承父类的接口 在此处有停下来思考，为何要这么做 */ zend_do_inherit_interfaces(ce, parent_ce TSRMLS_CC); /* 继承父类的属性 */ zend_hash_merge(&ce->default_properties, &parent_ce->default_properties, (void (*)(void *)) zval_add_ref, NULL, sizeof(zval *), 0); if (parent_ce->type != ce->type) { /* 用户自定义的类从内部类继承 */ zend_update_class_constants(parent_ce TSRMLS_CC); zend_hash_apply_with_arguments(CE_STATIC_MEMBERS(parent_ce) TSRMLS_CC, (apply_func_args_t)inherit_static_prop, 1, &ce->default_static_members); } else { zend_hash_apply_with_arguments(&parent_ce->default_static_members TSRMLS_CC, (apply_func_args_t)inherit_static_prop, 1, &ce->default_static_members); } zend_hash_merge_ex(&ce->properties_info, &parent_ce->properties_info, (copy_ctor_func_t) (ce->type & ZEND_INTERNAL_CLASS ? zend_duplicate_property_info_internal : zend_duplicate_property_info), sizeof(zend_property_info), (merge_checker_func_t) do_inherit_property_access_check, ce); /* 合并常量和成员函数 */ zend_hash_merge(&ce->constants_table, &parent_ce->constants_table, (void (*)(void *)) zval_add_ref, NULL, sizeof(zval *), 0); zend_hash_merge_ex(&ce->function_table, &parent_ce->function_table, (copy_ctor_func_t) do_inherit_method, sizeof(zend_function), (merge_checker_func_t) do_inherit_method_check, ce); do_inherit_parent_constructor(ce); if (ce->ce_flags & ZEND_ACC_IMPLICIT_ABSTRACT_CLASS && ce->type == ZEND_INTERNAL_CLASS) { ce->ce_flags |= ZEND_ACC_EXPLICIT_ABSTRACT_CLASS; } else if (!(ce->ce_flags & ZEND_ACC_IMPLEMENT_INTERFACES)) { /* The verification will be done in runtime by ZEND_VERIFY_ABSTRACT_CLASS */ zend_verify_abstract_class(ce TSRMLS_CC); } } |
关于上面do_inherit_parent_constructor(ce)
此方法实现魔术方法继承，如果子类中没有相关的魔术方法，则继承父类的对应方法。如下所示的PHP代码为子类没构造函数的情况
1 2 3 4 5 6 7 8 9 10 11 | class Base { public function __construct() { echo 'Base __construct<br />'; } } class Foo extends Base { } $foo = new Foo(); |
如上，会输出：Base __construct
显然继承了父类的构造方法，如果子类有自己的构造方法，并且需要调用父类的构造方法时，需要在子类的构造方法中调用父类的构造方法，PHP不会自动调用。
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