int a = 10; // 局部變量
void(^Global)(void) = ^{
    NSLog(@"Global");
};
void(^Malloc)(void) = ^{
    NSLog(@"Malloc,%d",a);
};
void(^__weak Stack)(void) = ^{
    NSLog(@"Stack,%d",a);
};
NSLog(@"%@",Global); // <__NSGlobalBlock__: 0x101aa80b0>
NSLog(@"%@",Malloc); // <__NSMallocBlock__: 0x600003187900>
NSLog(@"%@",Stack); // <__NSStackBlock__: 0x7ff7b12c22f0>

#import <Foundation/Foundation.h>
void test() {
    int a = 10;
    void(^Malloc)(void) = ^{
        NSLog(@"%d",a);
    };
}

struct __test_block_impl_0 {
  struct __block_impl impl;
  struct __test_block_desc_0* Desc;
	// 內(nèi)部存儲(chǔ)了變量a
  int a;
	/// 初始化函數(shù)。包含三個(gè)參數(shù)
	// - Parameters:
  ///   - fp: 函數(shù)指針
  ///   - desc: 描述
  ///   - _a: flag
  __test_block_impl_0(void *fp, struct __test_block_desc_0 *desc, int _a, int flags=0) : a(_a) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};
// 創(chuàng)建Malloc閉包，傳入?yún)?shù)如下
// fp: (void *)__test_block_func_0
// desc: &__test_block_desc_0_DATA
// _a: 變量a的值（值拷貝）
void(*Malloc)(void) = ((void (*)())&__test_block_impl_0((void *)__test_block_func_0, &__test_block_desc_0_DATA, a));
// __test_block_func_0實(shí)現(xiàn)如下
static void __test_block_func_0(struct __test_block_impl_0 *__cself) {
  int a = __cself->a; // bound by copy
			NSLog(···);
    }

void *_Block_copy(const void *arg) {
    return _Block_copy_internal(arg, true);
}
static void *_Block_copy_internal(const void *arg, const bool wantsOne) {
    struct Block_layout *aBlock;
		···
		// 類型強(qiáng)轉(zhuǎn)為Block_layout
    aBlock = (struct Block_layout *)arg;
		···
    // Its a stack block.  Make a copy.
		// 分配內(nèi)存
		struct Block_layout *result = malloc(aBlock->descriptor->size);
		if (!result) return NULL;
		memmove(result, aBlock, aBlock->descriptor->size); // bitcopy first
		// reset refcount
		result->flags &= ~(BLOCK_REFCOUNT_MASK|BLOCK_DEALLOCATING);    // XXX not needed
		result->flags |= BLOCK_NEEDS_FREE | 2;  // logical refcount 1
		// isa重新標(biāo)記為Malloc Block
		result->isa = _NSConcreteMallocBlock;
		_Block_call_copy_helper(result, aBlock);
		return result;
}

struct Block_layout {
    void *isa;  // isa指針
    volatile int32_t flags; // contains ref count
    int32_t reserved; // 保留位
    void (*invoke)(void *, ...); // call out funtion
    struct Block_descriptor_1 *descriptor;
};

self.name = @"YK";
__weak typeof(self) weakSelf = self;
self.block = ^{
    __strong typeof(self) strongSelf = weakSelf;
    strongSelf.callFunc();
};

#import <Foundation/Foundation.h>
void test() {
    __block int a = 10;
    void(^Malloc)(void) = ^{
        a++;
        NSLog(@"%d",a);
    };
    Malloc();
}

// 可以看到傳入的第三個(gè)參數(shù)，是__Block_byref_a_0結(jié)構(gòu)體類型的a變量地址，而不是上面講過的直接存儲(chǔ)int類型
void(*Malloc)(void) =
((void (*)())&__test_block_impl_0((void *)__test_block_func_0,
                                  &__test_block_desc_0_DATA,
                                  (__Block_byref_a_0 *)&a,
                                  570425344));
// __test_block_impl_0結(jié)構(gòu)體中存儲(chǔ)的變量也是__Block_byref_a_0類型
struct __test_block_impl_0 {
  struct __block_impl impl;
  struct __test_block_desc_0* Desc;
  __Block_byref_a_0 *a; // by ref
  __test_block_impl_0(void *fp, struct __test_block_desc_0 *desc, __Block_byref_a_0 *_a, int flags=0) : a(_a->__forwarding) {
    impl.isa = &_NSConcreteStackBlock;
    impl.Flags = flags;
    impl.FuncPtr = fp;
    Desc = desc;
  }
};
// 初始化__Block_byref_a_0如下
__attribute__((__blocks__(byref))) __Block_byref_a_0 a =
{(void*)0,
        (__Block_byref_a_0 *)&a,
        0,
        sizeof(__Block_byref_a_0),
        10};
// __Block_byref_a_0結(jié)構(gòu)體
struct __Block_byref_a_0 {
  void *__isa;
__Block_byref_a_0 *__forwarding; // 指針指向原始值
 int __flags;
 int __size;
 int a; // 值拷貝存儲(chǔ)
};

int a = 1;
__block int b = 2;
void(^Malloc)(void) = ^{
    NSLog(@"a,%d",a);
    NSLog(@"b,%d",b);
};
a = 3;
b = 4;
Malloc();
// 輸出結(jié)果如下
// a,1
// b,4

// 未調(diào)用swift_allocObject
let closure1 = { () -> () in
    print("closure1")
}
// 調(diào)用swift_allocObject
let a = 10
let closure2 = { () -> () in
    print("closure2 \(a)")
}

var variable = 10
let closure = { () -> () in
    variable += 1
    print("closure \(variable)")
}
closure() // closure 11
print(variable) // 11

var variable = 10
let closure = { [variable] () -> () in
    variable += 1
    print("closure \(variable)")
}
closure()
print(variable)

class YKClass {
    var name = "old"
}
let demoS = YKStruct()
let demoC = YKClass()
let closure1 = { [demoC] () -> () in
    demoC.name = "new"
    print("closure1 \(demoC.name)")
}
closure1() // closure1 new
print(demoC.name) // new
let closure2 = { () -> () in
    demoC.name = "new2"
    print("closure2 \(demoC.name)")
}
closure2() // closure2 new2
print(demoC.name) // new2