C++20 extends the using declaration to enum class. using enum introduces all the enum constants
into the current scope.
enum class rgbaColorChannel { red, green, blue, alpha };
std::string_view toString(rgbaColorChannel channel) {
switch (channel) {
using enum rgbaColorChannel;
case red: return "red";
case green: return "green";
case blue: return "blue";
case alpha: return "alpha";
}
}
As with other using declarations, using enum improves readability when used in small scopes yet it generates confusion in
large scopes.
The switch statement, as in the example above, is a natural scope for using enum.
This rule reports scopes that use a particular enum class extensively and can benefit from using enum declaration. For
example, it reports most switch statements applied to an enum value.
Exceptions
The rule does not apply if adding the using enum clause would create a name collision or reduce readability by shadowing a name.
