string = string + int:幕后是什么?

问题描述

在 C# 中，您可以隐式连接一个字符串，比如一个整数:

In C# you can implicitly concatenate a string and let's say, an integer:

string sth = "something" + 0;

我的问题是:

1. 为什么，假设您可以隐式连接字符串和整数，C# 不允许像这样初始化字符串:

1. Why, by assuming the fact that you can implicitly concatenate a string and an int, C# disallows initializing strings like this:

string sth = 0; // Error: Cannot convert source type 'int' to target type 'string'

C# 如何将 0 转换为字符串.是 0.ToString() 还是 (string)0 还是别的什么?

How C# casts 0 as string. Is it 0.ToString() or (string)0 or something else?

推荐答案

它编译为对 String.Concat(object, object)，像这样:

It compiles to a call to String.Concat(object, object), like this:

string sth = String.Concat("something", 0);

(注意这一行实际上会被编译器优化掉)

(Note that this particular line will actually be optimized away by the compiler)

该方法定义如下:(摘自.Net参考源)

This method is defined as follows: (Taken from the .Net Reference Source)

    public static String Concat(Object arg0, Object arg1) {
        if (arg0==null) {
            arg0 = String.Empty;
        }

        if (arg1==null) {
            arg1 = String.Empty;
        }
        return Concat(arg0.ToString(), arg1.ToString());
    }

(这调用了String.Concat(string, string))

要发现这一点，您可以使用 ildasm 或 Reflector(在 IL 或 C# 中，没有优化)来查看 + 行编译成什么.

To discover this, you can use ildasm, or Reflector (in IL or in C# with no optimizations) to see what the + line compiles to.

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