同时拥有NSMutableString和NSString的目的是什么? [英] What is the purpose of having both NSMutableString and NSString?

问题描述

为什么目标C同时提供NSString类和NSMutableString子类，而不是仅提供NSMutableString? NSString不等于"const NSMutableString"吗?

Why does Objective C provide both class NSString and subclass NSMutableString rather than just provide NSMutableString? Isn't a NSString equivalent to "const NSMutableString"?

在C ++中，只有一个字符串类std :: string，如果要使用常量，则可以声明const std:string.

In C++, you have only one string class, std::string, and if you want a constant you declare a const std:string.

我很想知道为什么我不应该只在各处使用NSMutableString，而从不理会NSString吗?必须有一个原因，否则语言设计者将不会同时提供两者.也许占用更少的存储空间?

I'm interested in knowing why I shouldn't just use NSMutableString everywhere and never bother with NSString? There must be a reason, or the language designers wouldn't provide both. maybe it takes up less storage or something?

推荐答案

两个类的原因与您有时使用std :: string和有时使用const std :: string的原因相同.但是，与C ++不同，Objective-C没有const方法，因此它们将const-和非const方法分成两个不同的类.在许多核心类中也可以看到这一点，例如NSArray(NSMutableArray)，NSDictionary(NSMutableDictionary)等.

The reason for both classes is the same reason that you sometimes use a std::string and sometimes use a const std::string. However, unlike C++, Objective-C doesn't have const methods, so they instead separate const- from non-const- methods into two different classes. This is also seen in many of the core classes, such as NSArray (NSMutableArray), NSDictionary (NSMutableDictionary), etc.

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