相关疑难解决方法(0)

我想声明一个返回指向同一类型函数的指针的函数.

我想用它来实现如下所示的状态机:

typedef event_handler_t (*event_handler_t)(event_t*); // compilation error

event_handler_t state2(event_t* e);
event_handler_t state1(event_t* e) {
    switch(e->type) {
    //...
    case SOME_EVENT:
        return state2;
    //...
    }

}
event_handler_t state2(event_t* e) {
    switch(e->type) {
    //...
    case OTHER_EVENT:
        return state1;
    //...
    }   
}

//...
event_handler_t event_handler;
//...
event_handler(&e);
//...

我设法使用如下结构解决compliation错误:

typedef struct event_handler {
    struct event_handler (*func)(event_t *);
} event_handler_t;

但这会使返回声明更加复杂:

event_handler_t state2(event_t* e) {
{
    event_handler_t next_handler = {NULL};
    switch(e->type) {
    //...
    case OTHER_EVENT:
        next_handler.func = state1;
        break;
    //...
    } 
    return next_handler;
} …

EDIT2:

不.建议的答案是关于异步调用.我想要并需要同步调用,就像在普通的标准递归调用中一样.

编辑:

而

__unsafe_unretained void (^unsafe_apply)(UIView *, NSInteger) ;

在没有警告或错误的情况下编译,它在运行时失败,并将NULL存储到unsafe_apply中.

不过这个:

- (void) applyToView: (UIView *) view {

    UIColor * (^colorForIndex)(NSInteger) = ^(NSInteger index) {
        return [UIColor colorWithHue: ((CGFloat) index / 255.0f)
                          saturation: 0.5f
                          brightness: 0.5f
                               alpha: 1.0f] ;
    } ;

    void (^applyColors) (UIView *, NSInteger index) = ^(UIView * view, NSInteger index) {
        view.backgroundColor = colorForIndex(index) ;
    } ;

    void (^__block recurse_apply)(UIView *, NSInteger) ;

    void (^apply)(UIView *, NSInteger) = ^(UIView * view, NSInteger level) { …