Anonymous — Anonymous inner classes in Objective-C

While reading Growing Object-Oriented Software Guided by Tests, I was inspired by the authors' use of Java anonymous inner classes to try and achieve the same thing using the Objective-C runtime. This is the result.

To illustrate, here's a couple of Kiwi test cases:

@protocol FooBar <NSObject>
- (void)doFooBar;
@end

it(@"allows an instance method with no arguments and no return value to be defined", ^{
    __block BOOL called = NO;

    id<FooBar> fooBar = aa_instanceOf(@protocol(FooBar), ^{
        aa_implement(@selector(doFooBar), ^(id self){
            called = YES;
        });
    });
    [fooBar doFooBar];

    [[theValue(called) should] equal:theValue(YES)];
});

@protocol StatefulFooBar <NSObject>
@property (nonatomic, strong) NSString *nickname;
@end

it(@"allows you to build anonymous classes with state", ^{
    id<StatefulFooBar> fooBar = aa_instanceOf(@protocol(StatefulFooBar), ^{

        // @property nickname
        __block NSString *_nickname;
        aa_implement(@selector(nickname), ^(id self){
            return _nickname;
        });
        aa_implement(@selector(setNickname:), ^(id self, NSString *nickname){
            _nickname = nickname;
        });

        // -description
        aa_implement(@selector(description), ^(id<StatefulFooBar> self){
            return [NSString stringWithFormat:@"They call me '%@'", self.nickname];
        });

    });

    fooBar.nickname = @"Hello, world!";
    [[fooBar.description should] equal:@"They call me 'Hello, world!'"];
});