Does Objective-C use string pooling?

问题

I know that Java and C# both use a string pool to save memory when dealing with string literals.

Does Objective-C use any such mechanism? If not, why not?

回答1:

Yes, string literals like @"Hello world" are never released and they point to the same memory which means that pointer comparison is true.

NSString *str1 = @"Hello world";
NSString *str2 = @"Hello world";
if (str1 == str2) // Is true.

It also means that a weak string pointer won't change to nil (which happens for normal objects) since the string literal never gets released.

__weak NSString *str = @"Hello world";
if (str == nil) // This is false, the str still points to the string literal

来源：https://stackoverflow.com/questions/11556714/does-objective-c-use-string-pooling