替换block原有实现

main.m

#import <Foundation/Foundation.h>

typedef struct __block_impl {
    void *isa;
    int Flags;
    int Reserved;
    void *FuncPtr;
}__block_impl;

typedef void(^GlobalBlock)(void);

void hookFunc() {
    NSLog(@"hello world");
}

void HookBlockToPrintHelloWorld(id blk) {
    __block_impl *ptr = (__bridge __block_impl *)blk;
    ptr->FuncPtr = &hookFunc;
}

int main(int argc, const char * argv[]) {
 
    GlobalBlock blk = ^void() {
        
    };
    HookBlockToPrintHelloWorld(blk);
    blk();

    return 0;
}