通过类名与自身调用类方法 [英] Calling class methods via class name vs self

问题描述

假设我们有一个名为 Calculator 的类.其中有一个类方法，称为runProgram.如果我想调用这个类的方法，在类的实现里面，这两者有什么区别:

Suppose we have a class named Calculator. There's a class method in it, called runProgram. If I wanted to call this class method, inside the class's implementation, what would the difference between these two be:

[Calculator runProgram]

或

[self runProgram]

这两个是一样的吗?

推荐答案

如果在实例方法中:

[self runProgram]

这里的self表示对象实例本身，因此会产生运行时错误.你要使用

in this, self means the object instance itself, and thus it will generate a runtime error. You want to use

[[self class] runProgram]

相反.

但是，如果你从另一个类方法调用这个方法，那么

However, if you call this method from another class method, then

[self runProgram]

是正确的，因为现在 self 指的是类本身.我不鼓励使用

is correct, since now self refers to the class itself. I'd discourage to use

[Calculator runProgram]

因为类的子类会错误地调用超类(Calculator)的方法，而不是可能被覆盖的方法.

because then subclasses of the class would erroneously call the superclass' (Calculator's) method instead of a possibly overridden method.

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