如果 Int32 只是 int 的别名，那么 Int32 类如何使用 int? [英] If Int32 is just an alias for int, how can the Int32 class use an int?

问题描述

一直在浏览.NET Framework参考源的.NET源码，只是为了好玩.并发现了一些我不明白的东西.

Been browsing through .NET source code of .NET Framework Reference Source, just for fun of it. And found something I don't understand.

有一个 Int32.cs 文件，其中包含 Int32 类型的 C# 代码.不知何故，这对我来说似乎很奇怪.C# 编译器如何为 Int32 类型编译代码?

There is a Int32.cs file with C# code for Int32 type. And somehow that seems strange to me. How does the C# compiler compile code for Int32 type?

public struct Int32: IComparable, IFormattable, IConvertible {
    internal int m_value;

    // ... 
}

但这在 C# 中不是非法的吗?如果 int 只是 Int32 的别名，它应该无法使用 错误 CS0523:

But isn't this illegal in C#? If int is only an alias for Int32, it should fail to compile with Error CS0523:

struct1"类型的结构成员struct2 field"导致结构布局出现循环.

Struct member 'struct2 field' of type 'struct1' causes a cycle in the struct layout.

编译器有什么魔力，还是我完全偏离了轨道?

Is there some magic in the compiler, or am I completely off track?

推荐答案

这在 C# 中不是非法的吗?如果int"只是Int32"的别名，它应该无法编译并出现错误 CS0523.编译器有什么魔力吗?

isn't this illegal in C#? If "int" is only alias for "Int32" it should fail to compile with error CS0523. Is there some magic in the compiler?

是的；该错误在编译器中被故意抑制.如果所讨论的类型是内置类型，则完全跳过循环检查器.

Yes; the error is deliberately suppressed in the compiler. The cycle checker is skipped entirely if the type in question is a built-in type.

通常这种事情是非法的:

Normally this sort of thing is illegal:

struct S { S s; int i; }

在这种情况下，S 的大小是未定义的，因为无论 S 的大小是多少，它都必须等于自身加上 ​​int 的大小.没有这样的大小.

In that case the size of S is undefined because whatever the size of S is, it must be equal to itself plus the size of an int. There is no such size.

struct S { S s; }

在这种情况下，我们没有任何信息可以用来推断 S 的大小.

In that case we have no information from which to deduce the size of S.

struct Int32 { Int32 i; }

但在这种情况下，编译器提前知道 System.Int32 是四个字节，因为它是一种非常特殊的类型.

But in this case the compiler knows ahead of time that System.Int32 is four bytes because it is a very special type.

顺便说一下，C# 编译器(以及就此而言，CLR)如何确定一组结构类型何时为循环的细节非常有趣.我会尝试在某个时候写一篇关于此的博客文章.

Incidentally, the details of how the C# compiler (and, for that matter, the CLR) determines when a set of struct types is cyclic is extremely interesting. I'll try to write a blog article about that at some point.

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