NSException raise：format：作为方法中的最后一条语句 [英] NSException raise:format: as the last statement in a method

问题描述

我有这种方法：

+ (MHTwitterParser*)createParser:(NSString*)format {
    if ([format compare:@"json"] == NSOrderedSame) {
        return [[MHJsonTwitterParser alloc] init];
    }

    [NSException raise:@"Unknown format" format:@"Unknown format of parser"];
}

编译器抱怨：

Control may reach end of non-void function

这只是一个警告，但这并不重要。

It is just a warning, but it does not matter.

最明显的解决方法是在 [NSException之后添加 return nil; 提高：... 。

Obvious fix for that is to add for example return nil; after the [NSException raise: ....

但是，我认为这是不必要的（甚至会误导读者），因为抛出了异常，因此控制可能会到达非空函数的末尾并不是正确的。还是我想念某些东西...？仅仅是编译器不完善还是有一定的原因？

However, I think it is not needed (and is even misleading for readers), because the exception is thrown, so it is not true that "Control may reach end of non-void function". Or am I missing something ...? Is it only compiler imperfection or there is some considerable reason for this?

编译器是Apple LLVM编译器3.1

The compiler is Apple LLVM compiler 3.1

推荐答案

原因很简单。

对于编译器，方法 [NSException提高：... ] 是黑盒方法。它不知道该方法实际上会引发异常。

For the compiler, the method [NSException raise: ...] is a black box method. It doesn't know that the method will actually raise an exception.

如果将其与Java或C ++进行比较，它们的会抛出语句是一种语言功能，编译器在找到它时会确切知道会发生什么。在Obj-C中，情况有所不同，有时取决于运行时条件。请考虑以下内容。

If you compare it with Java or C++, their throw statements are a language feature and the compiler knows exactly what will happen when it finds it. In Obj-C it's different and sometimes it depends on runtime conditions. Consider the following.

NSException* exception = nil;

if (someCondition) {

   exception = [NSException exceptionWithName:...];
}

[exception raise];

编译器不会知道是否确实引发了异常。

The compiler won't know if the exception is really raised or not.

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