为什么 + 运算符在任何 null 参数时都不会抛出任何异常？

Question

抱歉我的无知，但我已经尝试了很长时间而没有对此做出合理的解释：为什么 + 运算符在任何参数为 null 时不会抛出任何异常；例如：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication4
{
    class Program
    {
        static void Main(string[] args) {

            string str = null;
            Console.WriteLine(str + "test");
            Console.ReadKey();
        }
    }
}

Answer 1

因为 C# 编译器在您的操作中将 + 运算符转换为 String.Concat method，并且此方法在您尝试连接 null.[=26= 时使用空字符串 "" ]

来自 documentation;

An Empty string is used in place of any null argument.

从 7.7.4 Addition operator

The binary + operator performs string concatenation when one or both operands are of type string. If an operand of string concatenation is null, an empty string is substituted. Otherwise, any non-string argument is converted to its string representation by invoking the virtual ToString method inherited from type object. If ToString returns null, an empty string is substituted.

也来自 reference source;

if (IsNullOrEmpty(str0))
{
     if (IsNullOrEmpty(str1))
     {
         return String.Empty;
     }
     return str1;
}

为什么 + 运算符在任何 null 参数时都不会抛出任何异常？

Why + operator doesn't throw any exception when any null parameters?

c#

string

null