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c++templatesenums
nishantjr
nishantjr

Reputation: 1830

Templates parametrized for enums

I want to do this:

template <enum Type>
class Message {
private:
     Type m_type
};

enum StdInMessages { PrintHello, Echo, ... };
class StdInMsg : Message<StdInMessages>
{ ... }

enum NetworkMessages { DoSomethingElse, Shutdown ... };
class NetworkMsg : Message<NetworkMessages>
{ ... }

Of course, the actual messages are slightly different

Why doesn't this work?

template <enum T> class ATemplate {};

I get this error

error: use of enum ‘T’ without previous declaration

Upvotes: 0

Views: 208

Answers (2)

Luchian Grigore
Luchian Grigore

Reputation: 258698

Because that's not valid syntax for a template unless what you're looking for is what Konrad answered.

You need to either use typename or class.

The following should do it:

enum X
{
   a
};

template <typename T> class ATemplate {};

ATemplate<X> A;

Upvotes: 1

Konrad Rudolph
Konrad Rudolph

Reputation: 546213

It works if enum T is declared beforehand:

enum T {
    foo, bar
};

template <enum T> // or simply `template <T>`
class ATemplate { };

int main() {
    ATemplate<foo> x;
}

But judging from the variable name T, this isn’t what you want. Since it’s hard to guess what exactly you want, you need to be more specific.

Upvotes: 2

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