How to Use `std::source_location` with Variadic Template Functions?

Utilizing std::source_location with Variadic Template Functions

Problem:

The C 20 feature std::source_location provides context information during function calls. However, its integration with variadic template functions poses challenges due to the fixed position of variadic arguments.

Failed Attempts:

• Placing source_location as the first parameter interferes with variadic arguments.
• Inserting source_location between variadic arguments disrupts caller expectations.

Solution using a Deduction Guide:

To resolve this issue, a deduction guide can be used:

<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>

By specifying a deduction guide, the compiler can infer the correct types for the variadic template function.

Test:

<code class="cpp">int main() {
    debug(5, 'A', 3.14f, "foo");
}</code>

This code compiles successfully and prints the provided arguments along with their source location.

DEMO: [link provided in original question]

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