Is this a good way to use static_cast<void>(0) for nothing?

Question

Imagine that we do not have the [[maybe_unused]] attribute in C++.

How we could use this ability before inventing this attribute (I mean, before C++17)?

I found one solution:

static_cast<void>(0)

But I'm not sure that is correct! Can you explain a better solution (doesn't show compiler warnings, and passes static code analyzer)?

Edit: I wrote just one example of casting to void (maybe_unused was one , and below is another and etc ...) :

obj.enabled() ? static_cast<void>(0) : obj.DoThat(); /*as title said doing nothing*/ 

so I mean static_cast(variable) too.

Answer 1

static_cast<void>(0)

But I'm not sure that is correct!

static_cast<void>(0) doesn't make much sense, but I presume you mean static_cast<void>(maybe_unused_variable);

It is correct in the sense that it is well-formed. The standard doesn't specify when a compiler will warn about unused variables (except for recommending that [[maybe_unused]] suppresses such warning), but a cast to void is a de-facto convention to signify potentially unused names.

Can you explain a better solution

As suggested by Human-Compiler and originally by Herb Sutter, you could call an empty function template:

template <typename T>
void unused(const T&){}

// usage
unused(maybe_unused_variable);