Annex D (normative) Compatibility features [depr]

D.20 Deprecated formatting [depr.format]

D.20.2 Formatting arguments [depr.format.arg]

template<class Visitor, class Context> decltype(auto) visit_format_arg(Visitor&& vis, basic_format_arg<Context> arg);
Effects: Equivalent to: return visit(std​::​forward<Visitor>(vis), arg.value);