OneOf.swift

import Foundation

extension Equatable {

    /// Whether `self` is contained in a list of other values.
    /// Variadic version, see the method below for the generic implementation.
    ///
    /// - Parameter others: The values that `self` should be checked against.
    /// - Returns: Whether or not `self` is one of the provided other values.
    func isOne(of others: Self...) -> Bool {
        return isOne(of: others)
    }

    /// Whether `self` is contained in a list of other values.
    /// Non-variadic version that accepts any sequence of the same type.
    ///
    /// - Parameter others: The values that `self` should be checked against.
    /// - Returns: Whether or not `self` is one of the provided other values.
    func isOne<T: Sequence>(of others: T) -> Bool where T.Element == Self {
        return others.contains(self)
    }

}