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Hacked Option<T> enabling pattern matching on C#
// Copyright (c) Kouji Matsui (@kekyo@mastodon.cloud)
// License under MIT.
using System.ComponentModel;
namespace TestApp;
public static class Option
{
public static readonly NoneOption None =
NoneOption.Value;
public static Option<T> Some<T>(T value) =>
new SomeOption<T>(value);
}
[EditorBrowsable(EditorBrowsableState.Never)]
public sealed class NoneOption : None
{
private NoneOption()
{
}
public override string ToString() =>
"None";
public static readonly NoneOption Value =
new NoneOption();
}
public abstract class Option<T>
{
public static implicit operator Option<T>(NoneOption none) =>
NoneOption<T>.Value;
}
public interface Some
{
void Deconstruct(out object? value);
}
public interface Some<T>
{
void Deconstruct(out T value);
}
public interface None
{
}
internal sealed class SomeOption<T> : Option<T>, Some<T>, Some
{
private readonly T value;
public SomeOption(T value) =>
this.value = value;
void Some.Deconstruct(out object? value) =>
value = this.value;
void Some<T>.Deconstruct(out T value) =>
value = this.value;
public override string ToString() =>
$"Some {(this.value is string str ? $"\"{str}\"" : this.value?.ToString() ?? "(null)")}";
}
internal sealed class NoneOption<T> : Option<T>, None
{
public NoneOption()
{
}
public override string ToString() =>
"None";
public static readonly Option<T> Value =
new NoneOption<T>();
}
// =====================================================================
public static Option<string> FooBar()
{
return Option.Some("ABC");
return Option.None;
}
switch (FooBar())
{
case Some(var str):
// ...
break;
case None:
// ...
break;
}
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