How to Apply a Function to Each Element in a Tuple of Vectors Using Metaprogramming?

Template Tuple: Calling a Function on Each Element

Your aim is to invoke a function on each element of a template tuple std::tuple<:vector>...>. Within the TupleOfVectors struct, you seek to implement the do_something_to_each_vec method, which iterates through each member vector and executes a specific function upon them.

Solution

Employing some meta-programming techniques can address this challenge elegantly. With a meta-function gen_seq that produces compile-time sequences and companion function templates, you can implement the following machinery:

<code class="cpp">namespace detail {
    template<int... is>
    struct seq { };

    template<int n int... is>
    struct gen_seq : gen_seq<n n is...> { };

    template<int... is>
    struct gen_seq : seq<is...> { };
}</is...></int...></n></int></int...></code>

<code class="cpp">#include <tuple>

namespace detail {
    template<typename t typename f int... is>
    void for_each(T& t, F f, seq<is...>) {
        auto l = { (f(std::get<is>(t)), 0)... };
    }
}

template<typename... ts typename f>
void for_each_in_tuple(std::tuple<ts...>& t, F f) {
    detail::for_each(t, f, detail::gen_seq<sizeof...>());
}</sizeof...></ts...></typename...></is></is...></typename></tuple></code>

You can leverage for_each_in_tuple as depicted below:

<code class="cpp">#include <string>
#include <iostream>

struct my_functor {
    template<typename t>
    void operator () (T& t) {
        std::cout  t(42, 3.14, "Hello World!");
    for_each_in_tuple(t, my_functor());
}</typename></iostream></string></code>

In your case, you could utilize it as follows:

<code class="cpp">template<typename... ts>
struct TupleOfVectors {
    std::tuple<:vector>...> t;

    void do_something_to_each_vec() {
        for_each_in_tuple(t, tuple_vector_functor());
    }

    struct tuple_vector_functor {
        template<typename t>
        void operator () (T const &v) {
            // Perform operations on the vector argument...
        }
    };
};</typename></:vector></typename...></code>

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