c# - 为什么原始数据类型在不包含 System 命名空间的情况下也能工作？

Question

我读到所有原语都属于 System 命名空间。如果我注释掉 using System 我希望我的程序中出现构建错误，但它运行成功。这是为什么？

Answer 1

这是因为 int 是 System.Int32 的别名，并且由于“Int32”已经以其 namespace 为前缀(即“完全限定”)，所以语法是合法的，无需在代码顶部指定 using System;。

MSDN下面的片段描述了这个概念-

Most C# applications begin with a section of using directives. This section lists the namespaces that the application will be using frequently, and saves the programmer from specifying a fully qualified name every time that a method that is contained within is used. For example, by including the line:

using System;

At the start of a program, the programmer can use the code:

Console.WriteLine("Hello, World!");

Instead of:

System.Console.WriteLine("Hello, World!");

System.Int32(又名“int”)就是后者。这是代码中的示例 -

//using System;

namespace Ns
{
    public class Program
    {
        static void Main(string[] args)
        {
            System.Int32 i = 2;    //OK, since we explicitly specify the System namespace
            int j = 2;             //alias for System.Int32, so this is OK too
            Int32 k = 2;           //Error, because we commented out "using System"
        }
    }
}

由于第 11 行不是完全限定的/别名是完全限定的类型，using System; 需要取消注释才能使错误消失。

其他引用资料-

• C#, int or Int32? Should I care?

• Built-In Types Table (C# Reference) (列出所有内置类型及其 .NET 框架等效项)