How can I apply functions to each element within a template tuple of vectors, effectively performing tasks like \"for each (N): do_something_to_vec()\"?

Template Tuple: Invoking Functions on Each Element

Within a template tuple comprising vectors of different types, the need often arises to perform a specific operation on each vector element.

Question:

How can a function be invoked on each element within a template tuple, enabling the execution of tasks such as "for each (N): do_something_to_vec()"?

Answer:

Employing a combination of C meta-programming techniques and function templates offers an elegant solution.

• Meta-Function: Introduce a meta-function gen_seq that generates compile-time integer sequences, encapsulated in the seq class template.

• Function Templates: Utilize these function templates:

  • for_each: Iterates through a given tuple, invoking a provided function on each element.
  • for_each_in_tuple: Provides a syntax-friendly wrapper for using for_each specifically on tuples.
• Usage:

In the context of the provided TupleOfVectors template, a do_something_to_each_vec method can be implemented as follows:

<code class="cpp">template<typename... Ts>
struct TupleOfVectors {
    std::tuple<std::vector<Ts>...> 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 &amp;v) {
            // Perform desired operations on the argument vector...
        }
    };
};</code>

• Alternative Syntax (C 14 ):

If C 14 or later is available, the for_each_in_tuple function can be updated to use std::integer_sequence.

• C 17 Simplification:

In C 17 or later, a concise syntax exists:

<code class="cpp">std::apply([](auto ...x){std::make_tuple(some_function(x)...);} , the_tuple);</code>

These solutions provide a flexible and efficient method for performing operations on each element within a template tuple, without the need for explicit loops or indices.

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