如何强制未使用的变量成为块的一部分？

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];
}

为了便于调试，强制将url作为objectFinalization上下文的一部分复制并作为objectFinalization的一部分传递的最简单方法是什么？

我能想出几个可能的答案，但没有一个给我留下好印象。我可以做NSLog(@"%@",url)，但那会导致吐痰。我可以做一个NSAssert(url,...);或if (url) {}，但这两个并不能真正表达我想要做的事情。

Answer 1

几年后，我找到了最简单的答案。在代码块内部，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];
}

如果您只想在调试中使用：

- (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];
}

Answer 2

在#ifdef debug.. #endif中封装对NSLog()的调用

Answer 3

我想到了一个更好的答案，但感谢@NSResponder让我这样想：

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

这使得代码看起来像这样：

- (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];
}