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c++templatesstd-functiontypename

typename keyword for std::function

I have a class

class Consumer
{
public:
    typedef std::function<void()> EventHandler;
    ...
};

which I would like to use in this as template

template<class Consumer>
class ConsumerGroup
{
public:
    typename Consumer::EventHandler EventHandler;
    ConsumerGroup(EventHandler handler);
};

But above one results compilation error saying EventHandler is not a type. How should I use typename keyword in this case?

Solution

  • You need a type alias for dependent Consumer::EventHandler.

    This should work:

    using EventHandler =  typename Consumer::EventHandler;

    for lower compiler versions(before C++11)

    typedef  typename Consumer::EventHandler EventHandler;