可为空类型是BCL，CLR还是两者都实现？

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前段时间，我认为Nullable 值类型是类，封装了值类型和对HasValue的定义。

Some time ago I thought that Nullable<> value types are classes, encapsulating value types and a bool to HasValue. With some implicit cast operador for null, just implemented at BCL.

但是作为一个结构，如何实现呢？ Nullable<>结构对于CLR是特殊的吗？

But being a struct, how this can be achieved? Nullable<> struct is "special" for CLR?

推荐答案

Nullable< T> 被定义为普通结构，但CLR中有特殊的钩子可以将 [mscorlib] System.Nullable`1 的实例装箱/拆箱为空，具体取决于 HasValue 属性。在此处

Nullable<T> is defined as a normal struct, but there's special hooks within the CLR to box/unbox an instance of [mscorlib]System.Nullable`1 to null according to the HasValue property. There's more details on this here