Declare a block method parameter without using a typedef

Question

Is it possible to specify a method block parameter in Objective-C without using a typedef? It must be, like function pointers, but I can't hit on the winning syntax without using an intermediate typedef:

typedef BOOL (^PredicateBlock_t)(int);
- (void) myMethodTakingPredicate:(PredicateBlock_t)predicate

only the above compiles, all these fail:

-  (void) myMethodTakingPredicate:( BOOL(^block)(int) ) predicate
-  (void) myMethodTakingPredicate:BOOL (^predicate)(int)

and I can't remember what other combinations I've tried.

http://goshdarnblocksyntax.com/ – Kyle Clegg Jun 30 '14 at 18:32 — Kyle Clegg, Jun 30 '14 at 18:32

score 240 · Accepted Answer · answered Mar 30 '11 at 13:32

240

- ( void )myMethodTakingPredicate: ( BOOL ( ^ )( int ) )predicate

answered Mar 30 '11 at 13:32

Macmade

52,708
13
106
123

9

+1, though a `typedef` should really be preferred for more complicated cases. – Fred Foo Mar 30 '11 at 13:35
3

`- ( void )myMethodTakingPredicate: ( BOOL ( ^ )( NSString *name, NSString *age ) )predicate { //How Should I Access name & age here...? }` – Mohammad Abdurraafay Sep 12 '11 at 08:01
6

Those are just parameter names. Just use them. – Macmade Sep 12 '11 at 08:48
1

@larsmans I agree, unless this particular predicate/block is used in a lot of places where it would be more clear to have it typedef'd. Apple has defined a number of blocks that were quite simple, but did so such that it was easy to find what they wanted in documentation. – mtmurdock Feb 29 '12 at 03:23
1

and how to pass a block to that function. – user4951 Nov 15 '12 at 18:14
1

Ugh. There is nothing intuitive about this syntax at all. :( – devios1 Feb 26 '14 at 01:30
@chaiguy It is if you know how to deal with function pointers. It's the same syntax, with ^ instead of * – Macmade Feb 26 '14 at 08:14
@Macmade That's the syntax I'm complaining about. Not criticizing your answer mind you; already +1'd. – devios1 Feb 26 '14 at 21:48
3

Strong recommendation! Name your variables. They will autocomplete into usable code. So replace `BOOL ( ^ )( int )` with `BOOL ( ^ )( int count )`. – funroll Sep 08 '14 at 19:48

Mohammad Abdurraafay · Answer 2 · 2012-04-22T10:04:06.537

67

This is how it goes, for example...

[self smartBlocks:@"Pen" youSmart:^(NSString *response) {
        NSLog(@"Response:%@", response);
    }];


- (void)smartBlocks:(NSString *)yo youSmart:(void (^) (NSString *response))handler {
    if ([yo compare:@"Pen"] == NSOrderedSame) {
        handler(@"Ink");
    }
    if ([yo compare:@"Pencil"] == NSOrderedSame) {
        handler(@"led");
    }
}

edited Apr 22 '12 at 10:04

answered Sep 13 '11 at 05:56

Mohammad Abdurraafay

1,042
8
17

Is there a reason you don't use the [NSString isEqualToString:] method? – orkoden Mar 22 '13 at 13:53
2

Nothing specific. I'm just use to use 'compare:' a lot. '[NSString isEqualToString:]' is a better way though. – Mohammad Abdurraafay Mar 25 '13 at 05:28
Do you need the word `response` in the `smartBlocks` method definition? Couldn't you just say `(NSString*))handler {`? – Ash Aug 24 '16 at 01:10
You may have `(NSString *)) handler`. That's valid as well. – Mohammad Abdurraafay Sep 03 '16 at 06:23

score 20 · Answer 3 · answered Sep 08 '14 at 19:59

20

http://fuckingblocksyntax.com

As a method parameter:

- (void)someMethodThatTakesABlock:(returnType (^)(parameterTypes))blockName;

answered Sep 08 '14 at 19:59

funroll

35,925
7
54
59

score 9 · Answer 4 · answered Jan 06 '13 at 23:02

Another example (this issue benefits from multiple):

@implementation CallbackAsyncClass {
void (^_loginCallback) (NSDictionary *response);
}
// …


- (void)loginWithCallback:(void (^) (NSDictionary *response))handler {
    // Do something async / call URL
    _loginCallback = Block_copy(handler);
    // response will come to the following method (how is left to the reader) …
}

- (void)parseLoginResponse {
    // Receive and parse response, then make callback

   _loginCallback(response);
   Block_release(_loginCallback);
   _loginCallback = nil;
}


// this is how we make the call:
[instanceOfCallbackAsyncClass loginWithCallback:^(NSDictionary *response) {
   // respond to result
}];

score 2 · Answer 5 · edited Jan 27 '18 at 00:09

2

Even more clear !

[self sumOfX:5 withY:6 willGiveYou:^(NSInteger sum) {
    NSLog(@"Sum would be %d", sum);
}];

- (void) sumOfX:(NSInteger)x withY:(NSInteger)y willGiveYou:(void (^) (NSInteger sum)) handler {
    handler((x + y));
}

edited Jan 27 '18 at 00:09

pkamb

33,281
23
160
191

answered May 07 '15 at 09:20

Hemang

26,840
19
119
186

Declare a block method parameter without using a typedef

5 Answers5

Linked

Related