"Extensions" for Objective-C - Coroutines, User Literals, Autoboxing
I was recently reading about an interesting way to extend the literal syntax and autoboxing of Objective-C. The article, OCUDL In Depth by Dustin Bachrach got me thinking. I enjoy the clarity and succinctness of the standard literal syntax but like Dustin am disappointed with its completeness (or lack thereof).
I have also been intrigued by the addition of User Defined Literals in the latest C++11. Adopting Objective-C++ to pull this in can be interesting as we will see in a bit. But before diving into C++ we should consider another option.
Clang now supports overloaded functions in C. Its not automatic but is made available with the addtion of a llvm annotation.
int i = 23;
char *cstr = "A c-string";
NSNumber *num = @(i);
NSString *str = @(cstr);
But annoyingly, autoboxing an id or other ObjC instance results in an exception. It also only works on basic literals and is not extensible.
The standard system falls short on a number of points.
- You can't box Objective C objects - trying to do so raises an exception.
- Nothing can be done with nil / Nil
- Structures and supported
- It isn't user extensible.
see http://clang.llvm.org/docs/ObjectiveCLiterals.html
NSRect rect = NSZeroRect;
NSValue *value = $(rect);
NSValue* __attribute__((overloadable)) box(NSRect rect) {
return [NSValue valueWithRect:rect];
}
http://www.preney.ca/paul/archives/636
inline NSURL *operator "" _url(const char *url_s, std::size_t len) {
return [NSURL URLWithString:@(url_s)];
}
-(void)alert
{
id result;
BEGIN_COROUTINE();
[[[UIAlertView alloc] initWithTitle:@"Alert One"
message:@"This is a message"
delegate:self
cancelButtonTitle:@"Cancel"
otherButtonTitles:@"OK", nil]
show];
YIELD();
result = RETURN_VALUE;
NSLog(@"Alert returns %@", result);
[[[UIAlertView alloc] initWithTitle:@"Alert Two"
message:@"This is a message"
delegate:self
cancelButtonTitle:@"Cancel"
otherButtonTitles:@"OK", nil]
show];
YIELD();
result = RETURN_VALUE;
NSLog(@"Alert returns %@", result);
END_COROUTINE();
}
- (void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex
{
[self resumeCoroutineForMethod:@selector(alert) returnValue:@(buttonIndex)];
}
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