What is the different between NSCFString and NSConstantString?

Question

I declare the object variable as a NSString But when I use the XCode to look into my object, I saw there are two type of String, it seems that the system automa

Answer 1

As far as I know, NSCFConstantString is an implementation of NSString that keeps the string data in code memory. Compiler creates instances of it when you use @"string" constants. You can use NSCFConstantString anywhere an NSString could be used due to subclass/superclass relationship, but obviously not the other way around.