Question

Possible Duplicate:
Objective-C Default Argument Value

I couldn’t find a way to define a default argument to a function in ios like you would normally do in C++. Is it possible in iOS? If not is there a work around recommended?

Answer 1

This isn’t possible in Objective-C. One option is to do something like this to get the same functionality:

- (void)someMethodThatTakesAString:(NSString *)string
{
    if (string == nil) string = @"Default Value";

    // Use string
}

If you’re looking for the ability to omit an argument altogether, the typical way that’s done in Objective-C is to have multiple methods with progressively more specific argument sets:

- (void)doSomethingWithOptionA:(BOOL)optionA andOptionB:(int)optionB
{
   // Do something using options to control exactly what's done
}

- (void)doSomethingWithOptionA:(BOOL)optionA
{
   [self doSomethingWithOptionA:optionA andOptionB:42]; // Where 42 is the default for optionB
}

- (void)doSomething;
{
    [self doSomethingWithOptionA:NO]; // NO is the default for optionA
}

Then if you want to doSomething with just the default arguments, you can just call -doSomething. If you want to set optionA, but don’t care about optionB, you can call -doSomethingWithOptionA: etc.

Finally, it’s worth noting that you can use C++ to write for iOS, and you can also mix Objective-C and C++ using Objective-C++. All that said, always think carefully about how best to do things within the environment you’re using. Don’t try to force C++ idioms and patterns onto Objective-C and Cocoa. They’re different and they’re meant to be that way. It’s often very easy to spot a C++ programmer who hasn’t given up C++ conventions when transitioning to writing Objective-C code, and that’s usually not a good thing.