Question

考虑以下代码：

- (void)downloadObjectUsingURL: (NSURL *)url;
{
    id file = [self createFileForURL: url];
    Finalization objectFinalization = ^() {
        // we don't access url here, but it would be handy to see it in the debugger
        [file close];
    }
    id request = [self buildRequestFromURL: url];
    [object download: request
              toFile: file
        finalization: objectFinalization];
}

强制url作为objectFinalization上下文的一部分进行复制的最简单方法是什么，作为objectFinalization的一部分进行复制和传递，以便于调试？

我可以想到一些可能的答案，但没有一个能让我感觉良好。我可以做NSLog(@"%@",url)，但这会引起呕吐。我可以NSAssert(url,...);或if (url) {}，但这两者都不能表达我想要做的事情。

Answer 1

将来电转至NSLog()

中的#ifdef debug.. #endif

Answer 2

我想到了一个更好的答案，但感谢@NSResponder让我这样思考：

#if DEBUG
#define FORCE(a) NSParameterAssert(YES || a)
#else
#define FORCE(a)
#endif

这使代码看起来像这样：

- (void)downloadObjectUsingURL: (NSURL *)url;
{
    id file = [self createFileForURL: url];
    Finalization objectFinalization = ^() {
        FORCE(urL);
        [file close];
    }
    id request = [self buildRequestFromURL: url];
    [object download: request
              toFile: file
        finalization: objectFinalization];
}

Answer 3

多年后，我发现了最简单的答案。在块内，使用：

(void)variable;

示例：

- (void)downloadObjectUsingURL: (NSURL *)url;
{
    id file = [self createFileForURL: url];
    Finalization objectFinalization = ^() {
        (void)url;
        [file close];
    }
    id request = [self buildRequestFromURL: url];
    [object download: request
              toFile: file
        finalization: objectFinalization];
}

如果您只想进入调试：

- (void)downloadObjectUsingURL: (NSURL *)url;
{
    id file = [self createFileForURL: url];
    Finalization objectFinalization = ^() {
#if DEBUG
        (void)url;
#endif
        [file close];
    }
    id request = [self buildRequestFromURL: url];
    [object download: request
              toFile: file
        finalization: objectFinalization];
}

如何强制将未使用的变量作为块的一部分？

3 个答案: