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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