Is it possible to call a member function for every type in a tuple?

问题

namespace details {
template <std::size_t I = 0, typename Tuple, typename Function, typename... Args>
typename std::enable_if<I == std::tuple_size<Tuple>::value, void>::type ForEach(Tuple &t, Function f, Args &... args) {}

template <std::size_t I = 0, typename Tuple, typename Function, typename... Args>
typename std::enable_if<(I < std::tuple_size<Tuple>::value), void>::type ForEach(Tuple &t, Function f, Args &... args) {
    f(std::get<I>(t), args...);
    ForEach<I + 1>(t, f, args...);
}
}

An implementation for ForEach functionality for all types of a tuple is above. It calls f(tuple_type, args...)

However I want something like tuple_type.f(args...) where f and args are template arguments.

f would be a member function of all the types in the tuple, taking args... as arguments.

template <typename... Types>
class TupleManager {
    std::tuple<Types...> t;
    template <typename Function, typename... Args>
    void ForEach(Function f, Args& ... args) {
         details::ForEach<>(t, f, args...);
    }
}

Clarification: f needs to be a member function, i.e a function that takes the same name for all types in the tuple.

Eg:

struct A {
    void foo() {
        std::cout << "A's foo\n";
    }
};
struct B : A {
    void foo() {
        std::cout << "B's foo\n";
    }
};

struct C : A {
    void foo() {
        std::cout << "C's foo\n";
    }
};

But now I can't pass foo. Passing &A::foo print's A's foo. The requirement is to print A'foo for object of A in the tuple, B's foo for object of B in the tuple, and C's foo for object of C in the tuple.

Demo

回答1:

The beauty of std::for_each is in its disassociation of function application (on the elements of the range) from iteration (of the range). As such, one doesn't pass the arguments of the call to std::for_each (except for the callee itself that is already passed via the range). Having that in mind, you might want to consider using a different version of for_each that is closer to the std one. Check this one for example: iterate over tuple.

If you're up to a generalisation, you may want to use Jonathan Müller's tuple_iterator. That enables application std algorithms on std::tuples just as if std::tuple were a std container. In particular, you can use std::for_each for your desirable iteration.

来源：https://stackoverflow.com/questions/43259803/is-it-possible-to-call-a-member-function-for-every-type-in-a-tuple

标签

c++

c++11

templates

tuples

sfinae