install-package OneOf
This library provides F# style discriminated unions for C#, using a custom type OneOf<T0, ... Tn>. An instance of this type holds a single value, which is one of the types in its generic argument list.
You can use this as a parameter type:
public void SetBackground(OneOf<string, ColorName, Color> backgroundColor) { ... }
//The method above can be called with either a string or an ColorName enum valyr or a Color instance.
//you could achieve a similar result with overloads, but if you have multiple parameters of different types you would find the number of overloads required would increase very rapidly...
Or as a return type:
public OneOf<User, InvalidName, NameTaken> CreateUser(string username)
{
if (IsValid(username)) return new InvalidName();
var user = _repo.FindByUsername(username);
if(user != null) return new NameTaken();
var user = new User(username);
_repo.Save(user);
return user;
}
//Typically you would have to make multiple the return types implement a base class or interface and then use casts to access the values.
You use the TOut Match(Func<T0, TOut> f0, ... Func<Tn,TOut> fn) method to get a value out. E.g.
public void SetBackground(OneOf<string, ColorName, Color> backgroundColor) {
Color c = backgroundColor.Match(
str => CssHelper.GetColorFromString(str),
name => new Color(name),
col => col
);
_window.BackgroundColor = c;
}
