Category、load、initialize 源码讲解

#import <Foundation/Foundation.h>
#import "ZXYPerson.h"
#import "ZXYPerson+Eat.h"
#import "ZXYPerson+Test.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        ZXYPerson *person = [[ZXYPerson alloc]init];
        [person run];
    }
    return 0;
}

static void 
attachCategories(Class cls, category_list *cats, bool flush_caches)
{
    // cls: [ZXYPerson class]
    // cats - category: 代表[ZXYPerson+Eat,ZXYPerson+Test]
    
    if (!cats) return;
    if (PrintReplacedMethods) printReplacements(cls, cats);

    bool isMeta = cls->isMetaClass();
    
    /**方法列表 **mlists  二维数组
     *[
     * [method_t,method_t],
     * [method_t,method_t]
     * ]
     */
    method_list_t **mlists = (method_list_t **)
        malloc(cats->count * sizeof(*mlists));
    
    /**属性列表 **proplists 二维数组
     *[
     * [property_t,property_t],
     * [property_t,property_t]
     * ]
     */
    property_list_t **proplists = (property_list_t **)
        malloc(cats->count * sizeof(*proplists));
    
    /**协议列表 **protolists 二维数组
    *[
    * [protol_t,protol_t],
    * [protol_t,protol_t]
    * ]
    */
    protocol_list_t **protolists = (protocol_list_t **)
        malloc(cats->count * sizeof(*protolists));

    // Count backwards through cats to get newest categories first
    int mcount = 0;
    int propcount = 0;
    int protocount = 0;
    int i = cats->count;
    bool fromBundle = NO;
    while (i--) {//最后面编译的分类会优先调用，i--，首先取最后一个分类
        
        auto& entry = cats->list[i];
        //将category里面的方法列表组都加入到一个数组中
        method_list_t *mlist = entry.cat->methodsForMeta(isMeta);
        if (mlist) {
            mlists[mcount++] = mlist;
            fromBundle |= entry.hi->isBundle();
        }
        //将category里面的属性列表组都加入到一个数组中
        property_list_t *proplist = 
            entry.cat->propertiesForMeta(isMeta, entry.hi);
        if (proplist) {
            proplists[propcount++] = proplist;
        }
        //将category里面的协议列表组都加入到一个数组中
        protocol_list_t *protolist = entry.cat->protocols;
        if (protolist) {
            protolists[protocount++] = protolist;
        }
    }
    
    //得到类里面的数据
    auto rw = cls->data();

    prepareMethodLists(cls, mlists, mcount, NO, fromBundle);
    // 将所有分类的对象方法，附加到类（对象）对象的方法列表中
    rw->methods.attachLists(mlists, mcount);
    free(mlists);
    if (flush_caches  &&  mcount > 0) flushCaches(cls);

    // 将所有分类的属性，附加到类（对象）对象的属性列表中
    rw->properties.attachLists(proplists, propcount);
    free(proplists);

    //将所有分类的协议，附加到类（对象）对象的协议列表中
    rw->protocols.attachLists(protolists, protocount);
    free(protolists);
}

    /**方法列表 **mlists  二维数组
    *[
    * [method_t,method_t],协议ZXYPerson+Test的方法test
    * [method_t,method_t] 协议ZXYPerson+Eat的方法Eat
    * ]
    *  addedCount = 2
    */
    void attachLists(List* const * addedLists, uint32_t addedCount) {
        if (addedCount == 0) return;

        if (hasArray()) {
            // many lists -> many lists
            uint32_t oldCount = array()->count;
            //因为ZXYPerson有一个方法run，所以oldCount为1 ，addCount两个分类共有两个方法，所以newCount = 3
            uint32_t newCount = oldCount + addedCount;
            
            //通过realloc方法重新分配内存，并分配newCount的空间大小
            setArray((array_t *)realloc(array(), array_t::byteSize(newCount)));
            array()->count = newCount;
            
            //array()->lists：返回原来的方法列表
            //void    *memmove(void *__dst, const void *__src, size_t __len);将src的array()->lists移到array()->lists + addedCount，因为addedCount = 2，相当于将array()->lists向后移动2位
            memmove(array()->lists + addedCount, array()->lists, 
                    oldCount * sizeof(array()->lists[0]));
            
            //addedLists:所有分类的方法列表
            //void    *memcpy(void *__dst, const void *__src, size_t __n); 将src的addedLists拷贝到dst的array()->lists（原来方法的列表）
            //相当于分类的方法列表拷贝到了原来的方法列表位置，而原来的方法列表位于前面
            memcpy(array()->lists, addedLists, 
                   addedCount * sizeof(array()->lists[0]));
        }
        else if (!list  &&  addedCount == 1) {
            // 0 lists -> 1 list
            list = addedLists[0];
        } 
        else {
            // 1 list -> many lists
            List* oldList = list;
            uint32_t oldCount = oldList ? 1 : 0;
            uint32_t newCount = oldCount + addedCount;
            setArray((array_t *)malloc(array_t::byteSize(newCount)));
            array()->count = newCount;
            if (oldList) array()->lists[addedCount] = oldList;
            memcpy(array()->lists, addedLists, 
                   addedCount * sizeof(array()->lists[0]));
        }
    }

//ZXYPerson
+ (void)initialize{
    
    NSLog(@"Person + initialize");
}

//ZXYPerson +Test
+ (void)initialize{
    
    NSLog(@"Person (Test1) + initialize");
}

//ZXYPerson+Eat
+ (void)initialize{
    
    NSLog(@"Person (Eat) + initialize");
}

//ZXYStudent
+ (void)initialize{
    
    NSLog(@"Student + initialize");
}

//ZXYStudent (Test)
+ (void)initialize{
    
    NSLog(@"Student (Test) + initialize");
}

//ZXYStudent (Eat)
+ (void)initialize{
    
    NSLog(@"Student (Eat) + initialize");
}