fholm's Option<T>

Option.cs

using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;

public struct Option<T> : IEquatable<Option<T>> {
  T    _value;
  bool _hasValue;

  public T Value {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get => _hasValue ? _value : ThrowInvalidOperationException();
  }

  public bool IsSome {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get => _hasValue;
  }

  public bool IsNone {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get => _hasValue == false;
  }

  public Option(T value) {
    _value    = value;
    _hasValue = true;
  }

  static T ThrowInvalidOperationException() {
    throw new InvalidOperationException();
  }

  public static Option<T> None {
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    get => default;
  }

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public static implicit operator Option<T>(T value) {
    return new Option<T>(value);
  }
  
  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public void Deconstruct(out T value) {
    value = Value;
  }

  public bool Equals(Option<T> other) {
    return _hasValue == other._hasValue && EqualityComparer<T>.Default.Equals(_value, other._value);
  }

  public override bool Equals(object obj) {
    return obj is Option<T> other && Equals(other);
  }

  public override int GetHashCode() {
    unchecked {
      return (EqualityComparer<T>.Default.GetHashCode(_value) * 397) ^ _hasValue.GetHashCode();
    }
  }
}