iOS 之动态运行时 runtime

前言：

最近研究runtime，觉得里面的东西好深，所以决定先把苹果提供的runtime.h文件简单的翻译一下，关于用法会在之后进行一些分享。

/* Types */

#if !OBJC_TYPES_DEFINED

/// An opaque type that represents a method in a class definition.
typedef struct objc_method *Method;

/// An opaque type that represents an instance variable.
typedef struct objc_ivar *Ivar;

/// An opaque type that represents a category.
typedef struct objc_category *Category;

/// An opaque type that represents an Objective-C declared property.
typedef struct objc_property *objc_property_t;

这四个type 分别是：
(类中不确定类型的一个方法)、(不确定类型的一个实例变量)、(不确定类型的一个类目)、(不确定的OC的属性声明)

struct objc_class {
    Class isa  OBJC_ISA_AVAILABILITY;

#if !__OBJC2__
    Class super_class                                        OBJC2_UNAVAILABLE;
    const char *name                                         OBJC2_UNAVAILABLE;
    long version                                             OBJC2_UNAVAILABLE;
    long info                                                OBJC2_UNAVAILABLE;
    long instance_size                                       OBJC2_UNAVAILABLE;
    struct objc_ivar_list *ivars                             OBJC2_UNAVAILABLE;
    struct objc_method_list **methodLists                    OBJC2_UNAVAILABLE;
    struct objc_cache *cache                                 OBJC2_UNAVAILABLE;
    struct objc_protocol_list *protocols                     OBJC2_UNAVAILABLE;
#endif

} OBJC2_UNAVAILABLE;
/* Use `Class` instead of `struct objc_class *` */

#endif

这是定义一个objc_class 结构体；

#ifdef __OBJC__
@class Protocol;
#else
typedef struct objc_object Protocol;
#endif

/// Defines a method
struct objc_method_description {
    SEL name;               /**< The name of the method */
    char *types;            /**< The types of the method arguments */
};

/// Defines a property attribute
typedef struct {
    const char *name;           /**< The name of the attribute */
    const char *value;          /**< The value of the attribute (usually empty) */
} objc_property_attribute_t;

这段代码，我理解的就是定义的两个结构体，关于结构体，有机会写一篇内容；

/* Functions */

/* Working with Instances */

/**
 * Returns a copy of a given object.
 *
 * @param obj An Objective-C object.
 * @param size The size of the object \e obj.
 *
 * @return A copy of \e obj.
 */
OBJC_EXPORT id object_copy(id obj, size_t size)
    __OSX_AVAILABLE_STARTING(__MAC_10_0, __IPHONE_2_0)
    OBJC_ARC_UNAVAILABLE;

/**
 * Frees the memory occupied by a given object.
 *
 * @param obj An Objective-C object.
 *
 * @return nil
 */
OBJC_EXPORT id object_dispose(id obj)
    __OSX_AVAILABLE_STARTING(__MAC_10_0, __IPHONE_2_0)
    OBJC_ARC_UNAVAILABLE;

/**
 * Returns the class of an object.
 *
 * @param obj The object you want to inspect.
 *
 * @return The class object of which \e object is an instance,
 *  or \c Nil if \e object is \c nil.
 */
OBJC_EXPORT Class object_getClass(id obj)
     __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);

/**
 * Sets the class of an object.
 *
 * @param obj The object to modify.
 * @param cls A class object.
 *
 * @return The previous value of \e object‘s class, or \c Nil if \e object is \c nil.
 */
OBJC_EXPORT Class object_setClass(id obj, Class cls)
     __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);

/**
 * Returns whether an object is a class object.
 *
 * @param obj An Objective-C object.
 *
 * @return true if the object is a class or metaclass, false otherwise.
 */
OBJC_EXPORT BOOL object_isClass(id obj)
    __OSX_AVAILABLE_STARTING(__MAC_10_10, __IPHONE_8_0);

/**
 * Returns the class name of a given object.
 *
 * @param obj An Objective-C object.
 *
 * @return The name of the class of which \e obj is an instance.
 */
OBJC_EXPORT const char *object_getClassName(id obj)
    __OSX_AVAILABLE_STARTING(__MAC_10_0, __IPHONE_2_0);

从/*Functions*/开始就是一些方法(都是实例方法)：

1、id object_copy(id obj, size_t size) 返回的是传过来的对象的一个副本，需要的参数是 一个OC的对象，和对象的大小

2、id object_dispose(id obj) 释放给定的对象的内存

3、Class object_getClass(id obj) 返回的是对象的类

4、Class object_setClass(id obj, Class cls) 设置对象的类，参数是要修改的对象，一个类对象

5、BOOL object_isClass(id obj) 返回对象是否一个类的对对象

6、const char *object_getClassName(id obj) 返回给定的对象的类名（备注：类名是这个对象的实例？）

/**
 * Returns a pointer to any extra bytes allocated with an instance given object.
 *
 * @param obj An Objective-C object.
 *
 * @return A pointer to any extra bytes allocated with \e obj. If \e obj was
 *   not allocated with any extra bytes, then dereferencing the returned pointer is undefined.
 *
 * @note This function returns a pointer to any extra bytes allocated with the instance
 *  (as specified by \c class_createInstance with extraBytes>0). This memory follows the
 *  object‘s ordinary ivars, but may not be adjacent to the last ivar.
 * @note The returned pointer is guaranteed to be pointer-size aligned, even if the area following
 *  the object‘s last ivar is less aligned than that. Alignment greater than pointer-size is never
 *  guaranteed, even if the area following the object‘s last ivar is more aligned than that.
 * @note In a garbage-collected environment, the memory is scanned conservatively.
 */
OBJC_EXPORT void *object_getIndexedIvars(id obj)
    __OSX_AVAILABLE_STARTING(__MAC_10_0, __IPHONE_2_0)
    OBJC_ARC_UNAVAILABLE;

/**
 * Reads the value of an instance variable in an object.
 *
 * @param obj The object containing the instance variable whose value you want to read.
 * @param ivar The Ivar describing the instance variable whose value you want to read.
 *
 * @return The value of the instance variable specified by \e ivar, or \c nil if \e object is \c nil.
 *
 * @note \c object_getIvar is faster than \c object_getInstanceVariable if the Ivar
 *  for the instance variable is already known.
 */
OBJC_EXPORT id object_getIvar(id obj, Ivar ivar)
     __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);

/**
 * Sets the value of an instance variable in an object.
 *
 * @param obj The object containing the instance variable whose value you want to set.
 * @param ivar The Ivar describing the instance variable whose value you want to set.
 * @param value The new value for the instance variable.
 *
 * @note \c object_setIvar is faster than \c object_setInstanceVariable if the Ivar
 *  for the instance variable is already known.
 */
OBJC_EXPORT void object_setIvar(id obj, Ivar ivar, id value)
     __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);

/**
 * Changes the value of an instance variable of a class instance.
 *
 * @param obj A pointer to an instance of a class. Pass the object containing
 *  the instance variable whose value you wish to modify.
 * @param name A C string. Pass the name of the instance variable whose value you wish to modify.
 * @param value The new value for the instance variable.
 *
 * @return A pointer to the \c Ivar data structure that defines the type and
 *  name of the instance variable specified by \e name.
 */
OBJC_EXPORT Ivar object_setInstanceVariable(id obj, const char *name, void *value)
    __OSX_AVAILABLE_STARTING(__MAC_10_0, __IPHONE_2_0)
    OBJC_ARC_UNAVAILABLE;

/**
 * Obtains the value of an instance variable of a class instance.
 *
 * @param obj A pointer to an instance of a class. Pass the object containing
 *  the instance variable whose value you wish to obtain.
 * @param name A C string. Pass the name of the instance variable whose value you wish to obtain.
 * @param outValue On return, contains a pointer to the value of the instance variable.
 *
 * @return A pointer to the \c Ivar data structure that defines the type and name of
 *  the instance variable specified by \e name.
 */
OBJC_EXPORT Ivar object_getInstanceVariable(id obj, const char *name, void **outValue)
    __OSX_AVAILABLE_STARTING(__MAC_10_0, __IPHONE_2_0)
    OBJC_ARC_UNAVAILABLE;

/* Obtaining Class Definitions */

/**
 * Returns the class definition of a specified class.
 *
 * @param name The name of the class to look up.
 *
 * @return The Class object for the named class, or \c nil
 *  if the class is not registered with the Objective-C runtime.
 *
 * @note \c objc_getClass is different from \c objc_lookUpClass in that if the class
 *  is not registered, \c objc_getClass calls the class handler callback and then checks
 *  a second time to see whether the class is registered. \c objc_lookUpClass does
 *  not call the class handler callback.
 *
 * @warning Earlier implementations of this function (prior to OS X v10.0)
 *  terminate the program if the class does not exist.
 */
OBJC_EXPORT Class objc_getClass(const char *name)
    __OSX_AVAILABLE_STARTING(__MAC_10_0, __IPHONE_2_0);

/**
 * Returns the metaclass definition of a specified class.
 *
 * @param name The name of the class to look up.
 *
 * @return The \c Class object for the metaclass of the named class, or \c nil if the class
 *  is not registered with the Objective-C runtime.
 *
 * @note If the definition for the named class is not registered, this function calls the class handler
 *  callback and then checks a second time to see if the class is registered. However, every class
 *  definition must have a valid metaclass definition, and so the metaclass definition is always returned,
 *  whether it’s valid or not.
 */
OBJC_EXPORT Class objc_getMetaClass(const char *name)
    __OSX_AVAILABLE_STARTING(__MAC_10_0, __IPHONE_2_0);