We've all been there: you get some NSDictionary from some JSON deserialization, you expect it to be an NSString:

NSString *middleName = dictionaryFromJSON[@"middle_name"];

Everything seems fine until you discover that the middleName is optional and sometimes null. And suddenly your middleName contains NSNull instead of NSString and your App crashes because you tried to call length on your NSNull object. So you end up writing something like this:

NSString *middleName = dictionaryFromJSON[@"middle_name"];
if (![middleName isKindOfClass:[NSString class]) {
	middleName = nil;
}

Lots of ugly code for a simple stupid check. Meet NSObject+Expectation:

NSString *middleName = [dictionaryFromJSON[@"middle_name"] nilUnlessIsKindOfClass:[NSString class]];

[object nilUnlessIsKindOfClass:aClass] returns object if it is indeed an object of aClass. Otherwise it returns nil.

But there is even a little bit more. Take this example:

NSInteger someIntegerValue = [dictionary[@"someIntegerValue"] integerValue];

We already learnt that we can make this crash proof by using our little helper:

NSInteger someIntegerValue = [[dictionary[@"someIntegerValue"] ifIsKindOfClass:[NSNumber class]] integerValue];

But actually we don't care if our object is an NSNumber. We are fine, as long a the object won't crash if we call integerValue on it. There is an selector for that:

NSInteger someIntegerValue = [[dictionary[@"someIntegerValue"] nilUnlessRespondsToSelector:@selector(integerValue)] integerValue];

Finally there is one last method so you are completely covered:

id<MyFancyProtocol> aObject = [dictionary[@"fancyObject"] nilUnlessConformsToProtocol:@protocol(MyFancyProtocol)];

The nilUnlessRespondsToSelector: can become handy when calling optional methods of a protocol. How often did you write code like this:

if ([self.delegate respondsToSelector:@selector(shouldAbortDownloading)]) {
	return [self.delegate shouldAbortDownloading];
} else {
	return NO;
}

This might become a one-liner like this:

return [[self.delegate nilUnlessRespondsToSelector:@selector(shouldAbortDownloading)] shouldAbortDownloading];

If you need a default value instead of nil we have something for you to:

NSInteger theAnswer =  [[@(42) unless:alternativeAnswer respondsToSelector:@selector(integerValue)] integerValue];

When alternativeAnswer responds to the integerValue selector it will return alternativeAnswer otherwise @(42).

Ther methods unless:isKindOfClass: and unless:conformsToProtocol are available to.

License: BSD