UnTup

A small C++20 library to flatten nested tuple-like objects into a single tuple of copies or references.

also known as

A sliiightly overengineered solution to a simple problem of having a single structured binding in a for loop that uses std::views::zip and std::views::enumerate.

Does

What is claims to do (no warranty though), constexpr-enabled. By default, performs some tests in compile-time, too.

Includes

untup::untie() - converts nested tuple-like objects into a tuple of references:

auto t = std::tuple{ std::pair{ 'c', 3.1415 }, 2 };
auto [ c, pi, two ] = untup::untie(t);
pi = 3.0; // t is changed!

untup::untup() - converts nested tuple-like objects into a tuple of copies:

auto t = std::tuple{ std::pair{ 'c', 3.1415 }, 2 };
auto [ c, pi, two ] = untup::untup(t);
pi = 3.0; // Ehm.. OK? `t` doesn't care

untup::views::flatten - a shortcut to std::views::transform that calls untup::untup() on the element of the range:

for (
    auto [ idx, e1, e2 ] : std::views::zip(v1, v2)
                           | std::views::enumerate
                           | untup::views::flatten
) println("{}: {} and {}", idx, e1, e2);
// Instead of
for (
    auto [ idx, pair ] : std::views::zip(v1, v2)
                         | std::views::enumerate
) {
    auto [ e1, e2 ] = pair; // Eww, why?
    println("{}: {} and {}", idx, e1, e2);
}

Preserves

Reference types when copying with untup::untup()!

Requires

At least C++20.

Known issues

Doesn't build as a module on GCC.
Headers in module global fragment could cause errors. Read how to fix that below.

Adding to your project

git clone this repo into your project. Add

set( UT_HEADERONLY ON ) # Only if you don't want the module
add_subdirectory( path/to/UnTup )

target_link_libraries( YourTarget UnTup ) # Or UnTup::UnTup

to your CMakeLists.txt. Use with #include <untup.hh> or import untup;.

Headers in global module fragment break the build!

Yeah I know. This is why you can specify CXX_STD_MODULE and CXX_STD_MODULE_TARGET to provide a name of your module that provides a standard library to your project. If you're using modules, you probably have it anyway. UnTup will import CXX_STD_MODULE; instead of including STL headers and If CXX_STD_MODULE_TARGET is set, CMake will link UnTup to it making sure the target under this name is built before it.

Alternatively

Just copy untup.hh somewhere in your project and #include it.

GregTheMadMonk/UnTup