Pattern

Pattern.cs

public class Pattern<TReturn>
	: List<(Type Type, Func<object, TReturn> Map)>
{
	public void Add<T>(Func<T, TReturn> map)
		=> Add((typeof(T), o => map((T)o)));

	public Pattern<TReturn> Default(TReturn val)
	{
		Add((object _) => val);
		return this;
	}
	
	public TReturn Match(object value)
	{
		var map = this.FirstOrDefault(x => x.Type.IsInstanceOfType(value)).Map;
		
		if (map == null)
			throw new NotImplementedException($"No map found for type '{value.GetType()}");
		
		return map(value);
	}
}

// Example
var pattern = new Pattern<string>
{
	(ArgumentNullException e) => $"Paramter '{e.ParamName}' was null",
	(DivideByZeroException _) => "Can't divide by zero",
}
.Default("Oops something went wrong");

// returns: Paramter 'some parameter' was null
pattern.Match(new ArgumentNullException("some parameter"));
// returns: Can't divide by zero
pattern.Match(new DivideByZeroException());
// returns: Oops something went wrong
pattern.Match(new Exception());