为什么原始数据类型可以在不包含 System 命名空间的情况下工作? [英] Why do primitive data types work without including the System namespace?

问题描述

我读到所有原语都属于 System 命名空间.如果我注释掉 using System，我希望我的程序中存在构建错误.但是，它运行成功.这是为什么?

I read that all primitives fall under the System namespace. If I comment out using System, I would expect there to be a build error in my program. However, it is running successfully. Why is this?

推荐答案

这是因为 int 是 System.Int32 的别名，而Int32"已经是以其命名空间为前缀(即完全限定")，语法是合法的，无需在代码顶部指定 using System; .

It's because int is an alias for System.Int32, and since the "Int32" is already prefixed with its namespace (ie. "fully qualified"), the syntax is legal without having to specify using System; at the top of your code.

下面的 MSDN 片段描述了这个概念-

The MSDN snippet below describes this concept-

大多数 C# 应用程序都以一段 using 指令开头.本节列出了应用程序将使用的命名空间经常，并使程序员免于指定完全限定的每次使用其中包含的方法时命名.为了例如，通过包含以下行:

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;

在程序开始时，程序员可以使用以下代码:

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

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

代替:

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

System.Int32(又名int")将是后者.这是代码中的一个示例 -

System.Int32 (aka "int") would be the latter. Here is an example of this in code -

//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/别名完全限定类型，using System; 需要取消注释才能消除错误.

Since line 11 is not fully qualified / aliasing a fully qualified type, using System; would need to be uncommented for the error to go away.

其他参考资料-

• C#、int 还是 Int32?我应该关心吗?

内置类型表(C# 参考)(列出所有内置类型及其 .NET 框架等效项)

Built-In Types Table (C# Reference) (Lists all the built-in types, and their .NET framework equivalents)

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