Xcode warning "Property access results unused - getters should not be used for side effects"

Question

I'm getting this warning when I'm calling a local routine.

My code is this:

-(void)nextLetter {
    // NSLog(@"%s", __FUNCTION__);
    currentLetter ++;
    if(currentLetter > (letters.count - 1))
    {
        currentLetter = 0;
    }
    self.fetchLetter;
}

I'm getting the warning on the self.fetchLetter statement.

That routine looks like this:

- (void)fetchLetter {
    // NSLog(@"%s", __FUNCTION__);
    NSString *wantedLetter = [[letters objectAtIndex: currentLetter] objectForKey: @"langLetter"];

    NSString *wantedUpperCase = [[letters objectAtIndex: currentLetter] objectForKey: @"upperCase"];    


.....   
}

I prefer to fix warning messages, is there a better way to write this?

Thanks!

Solution 1

The dot notation (i.e. self.fetchLetter) is meant for properties, not for arbitrary methods. The self.fetchLetter is being interpreted as "get the 'fetchLetter' property of 'self'," which isn't what you intend.

Just use [self fetchLetter] instead.

Solution 2

In newer Xcode versions, even the [object method]; may trigger the warning. But sometimes we actually do need to call a property and discard the result, for example when dealing with view controllers and we need to make sure the view is actually loaded.

So we were doing:

// Ensure view is loaded and all outlets are connected.
[self view];

This now also triggers the “Property access results unused - getters should not be used for side effects” warning. The solution is to let the compiler know it's done intentionally by casting the result type to void:

(void)[self view];

Solution 3

You're declaring fetchLetter using syntax like this?

@property (retain) id fetchLetter;

That looks wrong for what you're doing. Properties are intended to be variable accessors that (in the case of getters) don't have any side effects.

You should declare fetchLetter as a method, like so:

- (void) fetchLetter;

and access it using:

[self fetchLetter]

Comments

[ICL1901]

Hi Chris, I did declare fetchLetter as you suggest. I have now changed the declaration to [self fetchLetter] as you and Tom indicated.. I appreciate the understanding.

[Dov]

This workaround no longer applies in Xcode 6.3 (beta)

[Dov]

I mean calling the selector instead of using dot notation. It technically shouldn't have probably made a difference, and now Clang still treats it the same way. @DarkDust's answer actually expresses the semantic intent of calling a selector just for its side effects

[Tom Dalling]

@Dov That is certainly true for property accessor methods (such as [UIViewController view]), but this question doesn't involve those. Still, I guess it's useful to know for the people who arrived here by googling the error message.