Invoke intseq

A C++ programming course project regarding metaprogramming.

Problem statement

The goal of this project is to implement a certain generalization of std::invoke, so that it treats arguments of type std::integer_sequence in a special way.

In the header file invoke_intseq.h you should implement a template:

template <class F, class... Args>
template result_type invoke_intseq(F&& f, Args&&... args);

1. If none of the arguments is of type std::integer_sequence, the call to invoke_intseq(f, args...) should have the same effect as a call to std::invoke(f, args...).

2. If there is at least one such argument, the function f should be invoked for all possible combinations of elements encoded in the std::integer_sequence's. Formally, let args... be a sequence of arguments a_1, a_2, ..., a_n and let a_i be the first argument of type std::integer_sequence<T, j_1, j_2, ..., j_m>. Then invoke_intseq(f, a_1, ..., a_n) is defined as a series of recursive calls:

invoke_intseq(f, a_1, ..., a_{i - 1}, std::integral_constant<T, j_1>, a_{i + 1}, ..., a_n);
invoke_intseq(f, a_1, ..., a_{i - 1}, std::integral_constant<T, j_2>, a_{i + 1}, ..., a_n);
...
invoke_intseq(f, a_1, ..., a_{i - 1}, std::integral_constant<T, j_m>, a_{i + 1}, ..., a_n);

The return type of the main invoke_intseq call is

• void if f returns void,
• a type satisfying the std::ranges::range concept (aka a type we can iterate on) containing all results acquired as a result of applying f to the modified arguments in the order specified above.

Additional requirements

1. We require perfect forwarding of both f and args....
2. We require constexpr: invoke_intseq should be evaluated at compile time if all arguments (f and args...) are evaluated as such.

Formal requirements

The solution will be compiled on the students machine with the following command:

clang++ -Wall -Wextra -std=c++20 -O2 *.cc

The solution has to pass the example test invoke_intseq_exmpl.cc (correct output in invoke_intseq_exmpl.out).