2. Blocks

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_NSConcreteStackBlock; //栈区
_NSConcreteGlobalBlock; //.data数据区
_NSConcreteMallocBlock; //堆区
_Block_object_assign //retain
_Block_object_dispose //release

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将栈区的block复制到堆区，用_Block_copy方法，注册到autoreleasepool中，然后返回该对象

tmp = _Block_copy(tmp);
return objc_autoreleaseReturnValue(tmp);

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// id为objc_object类型的结构体指针
    typedef struct objc_object{
        Class *isa;
    } *id;
    
    // Class为objc_class类型的结构体指针，与id类型结构一致
    typedef struct objc_class{
        Class isa;
    } *Class;
    
    struct Test{
        Class isa;
        int a;
        int b;
    };
    
    struct class_t{
        struct class_t *isa;
        struct class_t *superclass;
        Cache cache;
        IMP *vtable;
        uintptr_t data_NEVER_USE;
    };

void (^block)(id obj);
    {
        id array = [NSMutableArray new];
        block = [ ^(id obj){
            [array addObject:obj];
            NSLog(@"array: %@",array);
        } copy ];
        
    }
    block([NSObject new]);
    block([NSObject new]);
    block([NSObject new]);

循环引用

typedef void(^Block)(void);
@interface Test: NSObject
{
    Block _block;
}
@end

@implementation Test

-(instancetype)init{
    self = [super init];
    // 改为弱引用方式即可避免
    id __weak weakSelf = self;
    _block = ^{
        NSLog(@"self = %@", self); //_block引用self，self拥有_block

        NSLog(@"_var = %@", _var); //也会引起循环引用，相当于间接截获了self
//使用_var等同于self->_var
// 这样即可避免
id __weak obj = _val;
    _block = ^{
        NSLog(@"_val = %@", obj);
    };
};
    
    return self;
}

-(void)dealloc{
    NSLog(@"dealloc");
}

@end

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id array = [NSMutableArray new];
    void (^add)(void) = ^{
        id obj = [NSObject new];
        [array addObject:obj];
    };
    add();
    NSLog(@"array: %@",array);

typedef int (^SumBlock)(int a, int b);
    
    __block int result = 0;
    SumBlock sum = ^(int a, int b){
        result = a + b;
        return result;
    };
    sum(1,2);
    NSLog(@"result: %d", result);

typedef int (^SumBlock)(int a, int b);
    
    SumBlock sum = ^(int a, int b){
        return a + b;
    };
    NSLog(@"sum: %d", sum(1, 1));

void (^block)(int a);
    block = ^(int a){
        NSLog(@"block var: %d",a);
    };
    block(10);

  ^{
        NSLog(@"block");
    }();
    
    ^(int a){
        NSLog(@"%d", a);
    }(10);
    
    int sum = ^(int a, int b){ return a + b; }(5, 1);
    NSLog(@"sum: %d", sum);