C++26: The Oxford Variadic Comma

5 days ago

C++26 deprecates ellipsis parameters without a preceding comma (P3176R1 proposal).
This change improves C compatibility, reduces confusion with template parameter packs, and preserves design space for future features.
Currently, C++ allows both `void foo(int, ...)` (C-compatible) and `void foo(int...)` (C++-only), but the latter is being deprecated.
The comma-less form has caused confusion, especially with template parameter packs and abbreviated function templates.
The deprecation affects syntax like `void f(int...)` and `void g(auto args...)`, recommending `void f(int, ...)` instead.
Standalone ellipsis parameters (`void f(...)`) remain valid.
The change is a deprecation, not removal, allowing for automated fixes.
This clears the way for future proposals like homogeneous variadic function parameters.

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