Block and Closure

Block_no_arc.m

#import <Foundation/Foundation.h>

@interface BCObject : NSObject
+ (int(^)(int, int))magicFunction:(int)seed;
+ (BOOL(^)(id))lengthValidator:(NSUInteger)validLength;
@end

@implementation BCObject

+ (int(^)(int, int))magicFunction:(int)seed {
    int salt = 13.0f;
    int (^result) (int , int) = ^ int (int a, int b) {
        return a * salt + seed * b;
    };
    // Copy it to heap for dynamic usage
    return Block_copy(result);
}

+ (BOOL(^)(id))lengthValidator:(NSUInteger)validLength {

    BOOL (^result) (id) =  ^ BOOL (id object) {
        if ([object respondsToSelector:@selector(length)]) {
            return [object length]==validLength;
        } else if ([object respondsToSelector:@selector(count)]) {
            return [object count]==validLength;
        } else {
            return NO;
        }
    };
    // Copy it to heap for dynamic usage
    return [[result copy] autorelease];
}

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // You cannot release the block ... bad
        //NSLog(@"%d", [BCObject magicFunction:19](1, 3));
        
        // You can release the block then ... good.
        int (^magic)(int, int) = [BCObject magicFunction:20];
        NSLog(@"%d", magic(12, 13));
        Block_release(magic);
        
        NSArray *array1 = @[@1, @2.5f, @YES];
        NSArray *array2 = @[@1, @3];
        // Blocks are already in the autorelease pool.
        NSLog(@"Array 1 is %@" , [BCObject lengthValidator:3](array1)?@"valid":@"invalid");
        NSLog(@"Array 2 is %@" , [BCObject lengthValidator:3](array2)?@"valid":@"invalid");
    }
    return 0;
}

Blocks.m

#import <Foundation/Foundation.h>

@interface BCObject : NSObject
+ (int(^)(int, int))magicFunction:(int)seed;
+ (BOOL(^)(id))lengthValidator:(NSUInteger)validLength;
@end

@implementation BCObject

+ (int(^)(int, int))magicFunction:(int)seed {
    int salt = 13.0f;
    return ^ int (int a, int b) {
        return a * salt + seed * b;
    };
}

+ (BOOL(^)(id))lengthValidator:(NSUInteger)validLength {
    
    return ^ BOOL (id object) {
        if ([object respondsToSelector:@selector(length)]) {
            return [object length]==validLength;
        } else if ([object respondsToSelector:@selector(count)]) {
            return [object count]==validLength;
        } else {
            return NO;
        }
    };
    
}

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSLog(@"%d", [BCObject magicFunction:19](1, 3));
        
        int (^magic)(int, int) = [BCObject magicFunction:20];
        NSLog(@"%d", magic(12, 13));
        
        NSArray *array1 = @[@1, @2.5f, @YES];
        NSArray *array2 = @[@1, @3];
        NSLog(@"Array 1 is %@" , [BCObject lengthValidator:3](array1)?@"valid":@"invalid");
        NSLog(@"Array 2 is %@" , [BCObject lengthValidator:3](array2)?@"valid":@"invalid");
    }
    return 0;
}