self-closure.cs

private sealed class Closure<T> {
  private readonly Action<T> _action;
  private readonly Action _closure;
  private T _value;

  public Closure(Action<T> action) {
    _action = action;
    _closure = Execute;
  }

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public void Clear() => _value = default;

  [MethodImpl(MethodImplOptions.AggressiveInlining)]
  public Action Prepare(T value) {
    _value = value;
    return _closure;
  }

  private void Execute() => _action(_value);
}