Hello,
I've hit a wall while experimenting with variadic functions and blocks. The
code works pretty well until the second block is executed. After that, it
crashes the next time va_arg() gets called. Here's the code:
#import <Foundation/Foundation.h>
typedef id (^fooBlock)(id result, NSError **error);
void blockStep(fooBlock firstBlock, ...);
int main(int argc, const char * argv[])
{
@autoreleasepool {
blockStep (
^ (id result, NSError **error) {
NSMutableString *value = [NSMutableString new];
[value appendString:@"One!"];
return value;
},
^ (id result, NSError **error) {
NSMutableString *value = [NSMutableString new];
if (nil != result) {
[value appendString:result];
[value appendString:@", "];
}
[value appendString:@"Two!"];
return value;
}
);
}
return 0;
}
#pragma mark -
void blockStep(fooBlock firstBlock, ...)
{
va_list args;
va_start(args, firstBlock);
id result = nil;
do {
result = firstBlock(result, nil);
NSLog(@"%@", result);
} while (nil != (firstBlock = va_arg(args, fooBlock)));
va_end(args);
}
The output looks like this:
> 2012-07-04 16:18:40.000 BlockStep[12418:303] One!
> 2012-07-04 16:18:56.533 BlockStep[12418:303] One!, Two!
I've eliminated the crash by adding a nil sentinel in blockStep():
blockStep (
^ (id result, NSError **error) {
NSMutableString *value = [NSMutableString new];
[value appendString:@"One!"];
return value;
},
^ (id result, NSError **error) {
NSMutableString *value = [NSMutableString new];
if (nil != result) {
[value appendString:result];
[value appendString:@", "];
}
[value appendString:@"Two!"];
return value;
},
nil
);
This allows it to work without crashing, but I'd like if possible to avoid
having to place the sentinel. Any ideas?
Thanks in advance,
-- Tito
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