In Objective-c what I should use to return that parameter can't be nil?

Question

I know that I can return that parameter can't be nil by NSError or throw NSException, but what is the best option to inform that parameter can't be nil in objective-c ?

Answer 1

Documentation.

Use assertions to raise exceptions during development.

Return an NSError too (though it should hopefully never happen by the time you get to production).

Answer 2

You could use NSAssert(), which will only fire in builds where NS_BLOCK_ASSERTIONS is not defined:

- (void)someMethodWithParam:(id)someParam {
    NSAssert(someParam, @"someParam cannot be nil");
    ...
}

That will pretty much restrict the checking to you, and fellow developers, but if you want it to persist, regardless of build, then an NSException is best:

- (void)someMethodWithParam:(id)someParam {
    if (!someParam) {
        [NSException raise:@"MyException" format:@"someParam cannot be nil"];
    }
    ...
}

Answer 3

To check at compile time use

__attribute__ with nonnull

Example, first and second parameters should not be null:

extern void * my_memcpy (void *dest, const void *src, size_t len) 
__attribute__((nonnull (1, 2)));

The nonnull attribute specifies that some function parameters should be non-null pointers. Using nonnull encodes expectations about values into an explicit contract, which can help catch any NULL pointer bugs lurking in any calling code. Remember: compile-time errors ≫ run-time errors.

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