gregthemadmonk / untup

Flatten nested tuple-like objects in your C++20 code as much as you want!

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.