block_examples.m

#import <Foundation/Foundation.h>
#import <stdio.h>

@interface ExampleObject : NSObject

// BLOCK AS A PROPERTY
// -------------------
//
// @property (copy, ...) return_type (^block_name)(parameter_types);
//
@property (nonatomic, copy) NSInteger (^mungeTwoIntegers)(NSInteger, NSInteger);

// BLOCK AS A METHOD PARAMETER
// ---------------------------
//
// - (...)methodName:(return_type (^)(parameter_types))methodParamName;
//
- (void)setMungeBlock:(NSInteger (^)(NSInteger, NSInteger))aBlock;

// BLOCK AS RETURN VALUE
// ---------------------
//
// - (return_type (^)(parameter_types))methodName
// - (return_type (^)(parameter_types))methodNameWithParams:...
//
- (NSInteger (^)(NSInteger, NSInteger))makeMungeBlockWithMultiplier:(NSInteger)multiplier;

@end

@implementation ExampleObject

// BLOCK AS A METHOD PARAMETER
// ---------------------------
//
// - (...)methodName:(return_type (^)(parameter_types))methodParamName;
//
- (void)setMungeBlock:(NSInteger (^)(NSInteger, NSInteger))aBlock
{
    self.mungeTwoIntegers = aBlock;

    self.mungeTwoIntegers = ^NSInteger (NSInteger a, NSInteger b) {
        NSInteger munged = aBlock(a, b);
        printf("Munging %ld and %ld returns %ld\n", a, b, munged);

        return munged;
    };
}

// BLOCK AS RETURN VALUE
// ---------------------
//
// Declaration: - (return_type (^)(parameter_types))methodName
// Return value: [^return_type (parameters) { ... } copy]
//
- (NSInteger (^)(NSInteger, NSInteger))makeMungeBlockWithMultiplier:(NSInteger)multiplier
{
    return [^NSInteger (NSInteger a, NSInteger b) { return multiplier * (a + b); } copy];
}

@end

int main(int argc, char** argv)
{
    @autoreleasepool
    {
        // BLOCK AS A LOCAL VARIABLE
        // -------------------------
        //
        // LHS: return_type (^block_name)(parameter_types)
        // RHS: ^return_type (parameters) { ... }
        //
        NSInteger (^myBlock)(NSInteger, NSInteger) = ^NSInteger (NSInteger a, NSInteger b) {
            return a + b;
        };

        ExampleObject *obj = [ExampleObject new];
        [obj setMungeBlock:myBlock];
        obj.mungeTwoIntegers(3, 4);

        // BLOCK AS METHOD ARGUMENT
        // ------------------------
        //
        // [target methodName:^return_type (parameters) { ... }];
        //
        [obj setMungeBlock:^NSInteger (NSInteger a, NSInteger b) {
            return (a * a) + (b * b);
        }];
        obj.mungeTwoIntegers(3, 4);

        [obj setMungeBlock:[obj makeMungeBlockWithMultiplier:7]];
        obj.mungeTwoIntegers(3, 4);
    }
}