How Can I Expand a Tuple's Elements as Arguments to a Variadic Template Function in C ?

Expanding a Tuple into Variadic Template Function Arguments

In C , variadic template functions allow for functions that accept a variable number of arguments of a specific type. A common challenge arises when needing to pass arguments stored in a tuple to a variadic template function. This question explores several approaches to resolving this issue.

std::apply in C 17

C 17 introduced the std::apply function, which provides a straightforward solution. It takes two arguments: a callable and a tuple, and expands the tuple's elements as arguments to the callable. The syntax is:

std::apply(the_function, the_tuple);

This approach is supported in Clang 3.9 and later versions.

Workaround for Templated Functions

For templated functions, a workaround exists that involves creating a lambda in combination with std::apply. The lambda can handle perfect forwarding, ensuring that lvalue and rvalue references are correctly passed.

std::apply([](auto &&... args) { my_func(args...); }, my_tuple);

General Solution

The above workarounds address the specific case of passing a tuple to a non-templated function. For more complex scenarios, such as passing overload sets or function templates, a more comprehensive solution is available at https://blog.tartanllama.xyz/passing-overload-sets/. This solution ensures proper handling of perfect forwarding, constexpr-ness, and noexcept-ness.

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