Thoughts on Time

Time.cs

abstract class TZ
{
	public abstract TimeSpan UTCOffset { get; }
}

sealed class BST : TZ
{
	public override TimeSpan UTCOffset => TimeSpan.FromHours(1);
}

sealed class UTC : TZ
{
	public override TimeSpan UTCOffset => TimeSpan.FromHours(0);
}

class Time<T>
	where T : TZ, new()
{
	public Time(long utcOffset)
	{
		_offset = utcOffset;
		_tz = new T();
	}

	public Time<U> To<U>() where U : TZ, new()
	{
		return new Time<U>(_offset);
	}

	public DateTime AsDateTime => DateTime.FromBinary(_offset) + _tz.UTCOffset;
	
	private long _offset;
	private T _tz;
}

void Main()
{
	var bst = new Time<BST>(DateTime.UtcNow.ToBinary());
	var utc = new Time<UTC>(DateTime.UtcNow.ToBinary());

	bst.AsDateTime.Dump();
	utc.AsDateTime.Dump();
	utc.To<BST>().AsDateTime.Dump();
}

The idea is that the timezone is part of the type of a time. This prevents a time in a given timezone being used accidentally as a value for a time in another timezone. It would probably work better in a language with a more expressive type system than C#.