字符串和整数，隐式和显式 [英] Strings and ints, implicit and explicit

问题描述

如果一位同事问我这个问题，并且在我脑子里迷茫的状态我没有答案：

Had a coworker ask me this, and in my brain befuddled state I didn't have an answer:

为什么你能这样做：

string ham = "ham " + 4;

但不是：

string ham = 4;

当连接时，如果有字符串转换的隐式转换/操作，当将分配为字符串时，为什么不一样？ （当然没有做一些运算符重载）

If there's an implicit cast/operation for string conversion when you are concatenating, why not the same when assigning it as a string? (Without doing some operator overloading, of course)

推荐答案

当连接编译器时会转换语句ham + 4 调用 String.Concat ，这需要两个对象参数，所以将值 4 装箱，然后调用 ToString 。

When concatenating the compiler turns the statement "ham" + 4 into a call to String.Concat, which takes two object parameters, so the value 4 is boxed and then ToString is called on that.

对于赋值，没有从 int 隐式转换为 string ，因此您不能将 4 分配给字符串而不显式转换它。

For the assignment there is no implicit conversion from int to string, and thus you cannot assign 4 to a string without explicitly converting it.

换句话说，编译器对两个赋值的处理方式截然不同，尽管它们在C＃中看起来非常相似。

In other words the two assignments are handled very differently by the compiler, despite the fact that they look very similar in C#.

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