How to ignore parameter pack arguments

Question

With the expression (void)var; we can effectively disable unused variable warnings.

However, how does that work with arguments in a parameter pack?

template<bool Debug = DebugMode, typename... Arg>
void log_debug(const Arg&... args) {
    if constexpr(Debug) {
        (std::clog << ... << args) << std::endl;
    } else {
        //ignore the arguments willingly when not in debug
        (void)args; // does not compile
    }
}

OT, but please note that parameter pack functions are *not* the same as variadic functions. Variadic functions are the old C functions like `printf` or similar. — Some programmer dude, Oct 02 '22 at 09:59
Which compiler gives you a warning for this code (with `(void)args;` removed)? They shouldn't do that in a `if constexpr` branch like this. You are using `args` in the other branch. — user17732522, Oct 02 '22 at 10:01
What nuisance are you experiencing when you simply delete the entire `else` block in this specific code when actually called? Your question should include that as part of a proper [mcve]. — WhozCraig, Oct 02 '22 at 10:01

score 3 · Accepted Answer · answered Oct 02 '22 at 10:05

I suggest using maybe_unused:

template<bool Debug = DebugMode, typename... Arg>
void log_debug([[maybe_unused]] Arg&&... args) {

If you for some reason don't want that, you could make a fold expression over the comma operator in your else:

} else {
    (..., (void)args);
}

How to ignore parameter pack arguments

1 Answers1