I have the following code which compiles successfully in c++14.
template<class T, class ...Args>
class B
{
public:
using AbcData = int;
};
template<typename ...Args>
class D : public B<float, Args...>
{
public:
AbcData m_abc;
};
But when compiled in c++17, it gives the following error.
error C2061: syntax error: identifier 'AbcData'
What is wrong with the code and how to fix this?
When the base class B class depends upon the template parameters, even though derived class D here type alias AbcData inherited from the B, using simply AbcData in D class, is not enough.
You need to be explicit, from where you have it
template<typename ...Args>
class D : public B<float, Args...>
{
public:
typename B<float, Args...>::AbcData m_abc; // --> like this
};
AbcData is not ambiguous, you can use D itself instead of the base class B<float, Args...> to make the name dependent. That might be more straight-forward.AbcData multiple times so i used using AbcData = B<float, Args...>::AbcData. it's working now. is there better alternative that is shorter and less specifying too much redundant details? i also have other data types from base class not just AbcData.typename before B and you can use using typename B<float, Args...>::AbcData; instead.
/Za, maybe they have an extension or something.