Block定义

TODO：

【记录】iOS中的Block的定义画出结构图

Block结构体定义

来源=官网源码
- Block_private.h
  - 旧：https://opensource.apple.com/source/libclosure/libclosure-38/Block_private.h
  - 新：https://opensource.apple.com/source/libclosure/libclosure-63/Block_private.h
- TODO：更新版，记得还有额外的属性，抽空也去整理过来

-> 合并后的最新的理解：

Block定义的代码

struct Block_layout {
    void *isa;
    volatile int32_t flags; // contains ref count
    int32_t reserved;
    void (*invoke)(void *, ...);
    struct Block_descriptor_1 *descriptor;
    // imported variables
};

// merged new layout
struct Block_descriptor {
    // Block_descriptor_1
    uintptr_t reserved;
    uintptr_t size;

    // Block_descriptor_2
    // requires BLOCK_HAS_COPY_DISPOSE
    void (*copy)(void *dst, const void *src);
    void (*dispose)(const void *);

    // Block_descriptor_3
    // requires BLOCK_HAS_SIGNATURE
    const char *signature;
    const char *layout;     // contents depend on BLOCK_HAS_EXTENDED_LAYOUT
};