Variadic Template + static array

Question

Here we go, I got a template class with variadic classes arguments, each class has its own id from an enum value, for example:

struct A
    {
        enum ETypeID
        { 
            Value = 244
        };
    };

(same pattern for some other classes)

now I got :

template<typename TypeList...>
struct TClass
{
    static int _IDs[sizeof(TypeList)...];
};

I can't figure out how to feed the static array with each ETypeID::Value from the given typelist.

Any help would greatly be appreciated

Vittorio Romeo · Accepted Answer · 2017-12-15 13:16:22Z

3

template<typename... TypeList>
struct TClass
{
    constexpr static int _IDs[sizeof...(TypeList)] = {TypeList::Value...};
};

constexpr is required for in-place static data member initialization
sizeof...(TypeList) evaluates to the number of elements in the TypeList... pack
For TypeList = {A, B, C}, TypeList::Value... expands to: A::Value, B::Value, C::Value

answered Dec 15, 2017 at 13:16

Vittorio Romeo

94.1k37 gold badges276 silver badges451 bronze badges

Sign up to request clarification or add additional context in comments.

1 Answer 1