Improving setNameWithFormat: in RAC

RACSignalTest.m

#import <XCTest/XCTest.h>

#define RACNameBlockFromFormat(...) (^NSString *{\
    return [NSString stringWithFormat:__VA_ARGS__]; \
})

@interface RACSignal : NSObject

- (instancetype)someOperatorWithObject:(NSObject *)object;

- (NSString *)name;

@end

@implementation RACSignal {
    NSString *(^_nameBlock)(void);
}

- (instancetype)someOperatorWithObject:(NSObject *)object
{
    return [self setNameBlock:RACNameBlockFromFormat(@"transformed using `someOperatorWithObject` with object %@", [object description])];
}

- (NSString *)name
{
    return _nameBlock();
}

- (instancetype)setNameBlock:(NSString *(^)(void))nameBlock
{
    __block NSString *cache;
    _nameBlock = [^NSString *{
        if(cache == nil)
        {
            cache = nameBlock();
        }
        return cache;
    } copy];
    return self;
}

@end


@interface Foo : NSObject
@property (nonatomic, assign) int descriptionRequestedCount;
@end

@implementation Foo

- (NSString *)description
{
    self.descriptionRequestedCount++;
    return @"<Foo 0xFOOBAR>";
}

@end

@interface RACSignalTest : XCTestCase
@end

@implementation RACSignalTest

- (void)testFooIsolated
{
    Foo *foo = [Foo new];
    XCTAssertTrue(foo.descriptionRequestedCount == 0, @"");
    [foo description];
    XCTAssertTrue(foo.descriptionRequestedCount == 1, @"");
    [foo description];
    XCTAssertTrue(foo.descriptionRequestedCount == 2, @"");
}

- (void)testWithSignal
{
    Foo *foo = [Foo new];
    
    RACSignal *signal = [[RACSignal new] someOperatorWithObject:foo];
    XCTAssertTrue(foo.descriptionRequestedCount == 0, @"");
    XCTAssertEqualObjects([signal name], @"transformed using `someOperatorWithObject` with object <Foo 0xFOOBAR>");
    XCTAssertTrue(foo.descriptionRequestedCount == 1, @"");
    XCTAssertEqualObjects([signal name], @"transformed using `someOperatorWithObject` with object <Foo 0xFOOBAR>");
    XCTAssertTrue(foo.descriptionRequestedCount == 1, @"");
}

@end