自由手記

No Overloading

The data type returned by a method, together with the data types of each of its param‐ eters in order, constitute that method’s signature. It is illegal for two methods of the same type (class method or instance method) to exist in the same class with the same name but different signatures.

So, for example, you could not have two MyClass instance methods called myMethod, one of which returns void and one of which returns an NSString. Similarly, you could not have two MyClass instance methods called myMethod:, both returning void, one taking a CGFloat parameter and one taking an NSString parameter. An attempt to vi‐ olate this rule will be stopped dead in its tracks by the compiler, which will announce a “duplicate declaration” error. The reason for this rule is that if two such conflicting methods were allowed to exist, there would be no way to determine from a method call to one of them which method was being called.

You might think that the issue could be decided by looking at the types involved in the call. If one myMethod: takes a CGFloat parameter and the other myMethod: takes an NSString parameter, you might think that when myMethod: is called, Objective-C could look at the actual argument and realize that the former method is meant if the argument is a CGFloat and the latter if the argument is an NSString. But Objective-C doesn’t work that way. There are languages that permit this feature, called overloading, but Objective- C is not one of them. 

我在这阐述一下这2个OO语言之间的一些异同:

1, 两者最大的相同便是: 都是从 C 演化而来的面向对象语言, 两者都兼容标准 C 语言.

2, 两者最大的不同便是: Objective C 是完全动态(运行时绑定)的，而 C++是部分动态的(编译时绑定和运行时绑定)。

Objective C 支持在运行时动态类型决议(dynamic typing)，动态绑定(dynamic binding)以及动态装载(dynamic loading)；