Returns the number of variants in the enum type T.

If T is not an enum, calling this function will not result in undefined behavior, but the return value is unspecified. Equally, if T is an enum with more variants than usize::MAX the return value is unspecified. Uninhabited variants will be counted.

Note that an enum may be expanded with additional variants in the future as a non-breaking change, for example if it is marked #[non_exhaustive], which will change the result of this function.

Examples

# #![feature(never_type)]
# #![feature(variant_count)]

use std::mem;

enum Void {}
enum Foo { A(&'static str), B(i32), C(i32) }

assert_eq!(mem::variant_count::<Void>(), 0);
assert_eq!(mem::variant_count::<Foo>(), 3);

assert_eq!(mem::variant_count::<Option<!>>(), 2);
assert_eq!(mem::variant_count::<Result<!, !>>(), 2);