How Can You Use `std::source_location` with Variadic Template Functions in C 20?

Overcoming Hindrances in Using std::source_location with Variadic Template Functions

Variadic template functions, a potent feature in C 20, allow for the handling of an arbitrary number of arguments. However, integrating std::source_location, a means to capture call context information, with these functions presents a challenge.

The Collision with Variadic Parameters

Variadic parameters must reside at the end of a function signature, posing a roadblock when incorporating std::source_location.

Solution 1: Implementing a Deduction Guide

This issue can be circumvented by introducing a deduction guide that transforms the call syntax:

<code class="cpp">template <typename... Ts>
struct debug
{
    debug(Ts&&... ts, const std::source_location& loc = std::source_location::current());
};

template <typename... Ts>
debug(Ts&&...) -> debug<Ts...>;</code>

In this setup, the function signature remains unchanged, while the deduction guide bridges the gap:

<code class="cpp">int main()
{
    debug(5, 'A', 3.14f, "foo"); // Call converted to debug<int, char, float, const char*>
}</code>

This solution retains the benefits of std::source_location and ensures seamless syntax for variadic template functions.

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