Why am I allowed to use the incomplete enum class?

Question

Why is the code below compiled without any errors?

enum class Enumeration;
void func()
{
    auto enumeration = static_cast<Enumeration>(2);
    auto value = static_cast<int>(enumeration);
}

Answer 1

It compiles because the compiler knows at compile time the size Enumeration(which turns out to be empty).

You clearly see this syntax:

 enum class Enumeration : short;

The compiler knows everything there is to know about Enumeration. Enumerationis opaque-enum-declaration , which also means that type completei.e. you can use sizeofon it. If necessary, you can specify a list of counters in a later version (unless, of course, re-recording with a different base type is required).

, enum class, static_cast .

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enum afterall.

cppreference

, static_cast .

: enum int?