Define template based on parameter pack values

Question

The methods in this class use an index sequence containing a sequence of indices covering the entire data tuple (an index for each argument passed in the parameter pack). Per other answers I've seen, I'm currently templating my methods as such:

#include 
#include 
#include 

using std::tuple;

template 
class Foo
{
    protected:
        tuple>...> data;

    private:

        template
        void _clear_(std::index_sequence) {
            (std::get(data)->clear(), ...);
        };

    public:

        void clear()
        { _clear_(std::index_sequence_for()); };
};

This seems messy, though. I was wondering if there's a way that I could define Is at a class-level scope (or, more generally, whether there's a better way to do this).

user_2684539 · Answer

With C++17, you might simply use std::apply:

void clear()
{
    std::apply([](auto&... vs){ (vs.clear(), ...); }, data);
}

I was wondering if there's a way that I could define Is at a class-level scope

With extra layer:

template  class FooImpl;

template 
class FooImpl, Ts...>
{
protected:
    std::tuple>...> data;

public:
    void clear() { (std::get(data).clear(), ...); };
};

template 
using Foo = FooImpl, Ts...>;

Define template based on parameter pack values

1 Answers