Dear Reader,

I would like to explore interesting features that will ship with C++26.

One such feature is pack-indexing.

The basic mechanics. If you have an unexpanded parameter pack Ts..., which consists T0, T1,...,T_{N-1}, you can simply write Ts...[I] to select T_I. I should be constexpr.

Moreover, if you have a pack Is..., for example <5,0,3>, then Ts...[Is]... expands to Ts[5], Ts[0], Ts[3].

#include <print>
#include <tuple>

template<typename... Ts>
constexpr auto first(Ts... args) -> Ts...[0]{
    return args...[0];
}

template<typename... Ts>
constexpr auto last(Ts... args) -> Ts...[sizeof...(Ts) - 1]{
    return args...[sizeof...(Ts) - 1];
}

template<size_t... Is, typename... Args>
constexpr auto select(Args&&... args){
    auto tup = std::forward_as_tuple(args...);
    return std::make_tuple(std::get<Is>(tup)...);
}

int main(){
    static_assert(first(1, 2, 3, 4, 5) == 1);
    static_assert(last(1, 2, 3, 4, 5) == 5);
    static_assert(select<2,1,0>(1, 2, 3, 4, 5) == std::tuple{3,2,1});
}

Compiler Explorer

This month, I solved few interesting coding exercises:

• Different ways to filter a container
• Coding Exercise - Grouping lines together
• Constructing a 3D array
• Implementing string and SSO

I want to continue sharing interesting C++/Rust/Zig code snippets, discuss about concurrency, performance aspects.

If you want to help, just hit the Reply button and tell me your C++ story. What are the topics you'd like to read more/nerd out?

Also, I appreciate any help: from finding typos, improving code samples to suggesting new content and even some forms of collaboration.

-- Quasar