The attribute-token maybe_unused indicates that a name or entity is possibly intentionally unused. It shall
appear at most once in each attribute-list and no attribute-argument-clause shall be present.
The attribute may be applied to the declaration of a class, a typedef-name, a variable (including a structured
binding declaration), a non-static data member, a function, an enumeration, or an enumerator.
For an entity marked maybe_unused, implementations should not emit a warning that the entity or its
structured bindings (if any) are used or unused. For a structured binding declaration not marked maybe_-
unused, implementations should not emit such a warning unless all of its structured bindings are unused.
A name or entity declared without the maybe_unused attribute can later be redeclared with the attribute
and vice versa. An entity is considered marked after the first declaration that marks it.
Example:
[[maybe_unused]] void f([[maybe_unused]] bool thing1, [[maybe_unused]] bool thing2)
{
[[maybe_unused]] bool b = thing1 && thing2;
assert(b);
}
Implementations should not warn that b is unused, whether or not NDEBUG is defined.