Item 10: Prefer Scoped enums to Unscoped enums
Scoped enums are better because they are scoped, strong-typed, and may be forward-declared out-of-the-box.
enum Shape {
rectangle, square, triangle
};
enum class Color {
black, white, red
};
//// Advantage 1: Scoped
// Error! Conflict with `rectangle` of `Shape`
auto rectangle = false;
// `Shape`'s members are polluting the scope containing it!
Shape s = rectangle;
// `white` won't conflict with Color::white
auto white = false;
// It must be accessed with scope
Color c = Color::white;
//// Advantage 2: Strong-typed
// Okay, implicitly convert to double
if (s < 1.9) {
...
}
// Error!
if (c < 1.9) {
...
}
Advantage 3: Scoped enums may be forward-declared out-of-the-box.
The reason is that the underlying type of scoped enums are default to int, while for unscoped enums you have to explicitly specify it.
(If you specify the underlying type for an unscoped enum, it may be forward declared.)
You may specify underlying type with this syntax form:
// Specify the underlying type and also forward-declare it
enum class Color: std::uint32_t;
enum Shape: std::uint32_t;
Advantage(?) of unscoped enum:
Unscoped enums are probably only useful in defining lists of integral constants at the global scope.
