User-defined variable types

Question

A useful construct in Delphi (Object Pascal) is:

type
TNumColors = 1..256;
var
numColors: TNumColors;

This defines numColors to a restricted range of integers and allows range checking.

How do you do this in C# please?

Jure · Answer

You can do this: int range_size = 256; int range_start = 1; int temp = /* your calculation */ - range_start numColors = temp % range_size + range_start and you can for example pack all this into a property: private int num_colors; private int range_size = 256; private int range_start = 1; public int NumColors { get { return num_colors; } set { num_colors = (value - range_start) % range_size + range_start; } } so now you can simply write: NumColors *= 1000; and it would set NumColors (num_colors indirectly) to your selected range (1-256). But modulo doesn't work as you want it to with negative numbers in your case. -1000 % 256 will return -1000 so you need to do 257 - |-1000| % 256  which in code is: public int NumColors { get { return num_colors; } set { value -= range_start; if (value num_colors = range_size - (-value % range_size) + range_start ; else num_colors = value % range_size + range_start; } } and now you can do this: NumColor -= 1000;

Sam Hobbs · Answer

Also note that Jure is doing more in his sample than what is done in your sample. For example you have the numbers 1..256 whereas Jure is showing you that it is better to use symbolic names. It is not necessary to do that in C# but most experienced programmers do things like that (use symbolic names) because they know from experience that it is often easier in the future. It is possible to do the equivalent of what Delphi does in less C# code so I wanted to make it clear that part of the reason that Jure's sample is so much larger is because Jure is showing you a sample of what should be done. The thing I don't know is the details of what Delphi does so I would be reluctant to provide a specific answer since I cannot be sure it would be equivalent. I don't know Delphi so I don't know what happens if a TNumColors object is set to a value that is outside the limits; Jure's code makes some assumptions about what should be done but if that is inconsistent with what Delphi does then I would try to get clarification of what Delphi does before posting something specific.

Jure · Answer

As Sam said there are different ways to implement this depending on what you need. I wrote an article about various approaches: Values caught in intervals I've also completely rewritten the code that's posted here it's simpler and works without modulus operation.

Mike Smith · Answer

Thanks Sam. I take your point about C# 'doing more'. I was really exploring C# rather than trying to 'translate' a specific concept for a particular program. I can't remember offhand how Delphi would respond to an infringement and I don't seem to be able to get my legacy compiler up and running to try it out. However I feel as Jure and you point out that C# makes explicit (in this case at least) what Delphi keeps as implicit and hidden behind the scenes. I'm all for the 'explicit' approach and perhaps I shouldn't try to be too clever! Thanks again to you both...

Mike Smith · Answer

Thanks Jure. I'll give your workout a whirl. Compared to the Delphi the C# answer does look much more complicated but I expect that C# is putting up front what Delphi hides behind the scenes so resulting in a cleaner picture overall. Mike

Sam Hobbs · Answer

Wow Delphi sure looks much more productive than C#. Something that can be done in just one line using Delphi takes many lines in C#. It seems foolish to use C#. Actually I think that Jure's samples do more than what the Delphi sample does. Delphi does appear to have a more productive range checking feature but I assume C# is as productive or more productive in other ways.