Find ALL cocoa classes that are singleton? - ios

Question

There are several system classes in Cocoa that are singletons, such as UIApplication, NSNotificationCenter. Now, I want to find all classes that are singleton, any suggestion that how could I quickly find them all?
I'm working on a huge codebase, and I need to separate the system singleton object from the customized singleton.

Answer 1

Objective-C runtime hackery! Fun!
Now, before I continue, I will present the disclaimer that I'd never recommend putting anything like this in actual shipping code, and that if you do, it's totally not my fault. This can be fun/interesting to do for educational purposes, though.
This isn't going to be an exact science, since the language itself doesn't have any actual concept of a "singleton". Basically, we're just looking for Objective-C classes that have class methods with certain giveaway prefixes. If we find one of those, there's a good chance that we have a singleton.
With that in mind:
#import <Foundation/Foundation.h>
#import <objc/runtime.h>
static BOOL ClassIsSingleton(Class class) {
unsigned int methodCount = 0;
Method *methods = class_copyMethodList(object_getClass(class), &methodCount);
#try {
for (unsigned int i = 0; i < methodCount; i++) {
Method eachMethod = methods[i];
// only consider class methods with no arguments
if (method_getNumberOfArguments(eachMethod) != 2) {
continue;
}
char *returnType = method_copyReturnType(eachMethod);
#try {
// only consider class methods that return objects
if (strcmp(returnType, #encode(id)) != 0) {
continue;
}
}
#finally {
free(returnType);
}
NSString *name = NSStringFromSelector(method_getName(methods[i]));
// look for class methods with telltale prefixes
if ([name hasPrefix:#"shared"]) {
return YES;
} else if ([name hasPrefix:#"standard"]) {
return YES;
} else if ([name hasPrefix:#"default"]) {
return YES;
} else if ([name hasPrefix:#"main"]) {
return YES;
} // feel free to add any additional prefixes here that I may have neglected
}
}
#finally {
free(methods);
}
return NO;
}
int main(int argc, const char * argv[]) {
#autoreleasepool {
NSMutableArray *singletons = [NSMutableArray new];
int classCount = objc_getClassList(NULL, 0);
Class *classes = (Class *)malloc(classCount * sizeof(Class));
#try {
classCount = objc_getClassList(classes, classCount);
for (int i = 0; i < classCount; i++) {
Class eachClass = classes[i];
if (ClassIsSingleton(eachClass)) {
[singletons addObject:NSStringFromClass(eachClass)];
}
}
}
#finally {
free(classes);
}
NSLog(#"Singletons: %#", singletons);
}
return 0;
}