A SQL-Like IN function for C# and VB.NET

Introduction

This tip presents helper functions similar to the SQL IN clause for use within .NET programs. The intention is to help avoid combining && / || (And / Or) within complex if statements.

Background

Some considerable time ago, I found myself having to write some fairly complex if-statements combining lots of Ands with a whole load of Ors. I very quickly found myself wishing that VB6 (I know, I know!) had something similar to the T-SQL construct IN so I could get rid of the "Ors" and simplify the logic.

So I wrote myself some helper functions to do just that. It really wasn't pretty, and fortunately, it has now been condemned to the annals of history (although it is probably still sitting on a backup server somewhere!).

Then recently, I came across a post in Quick Answers where the OP had a very similar problem. Here's a (very much) simplified example of what it looked like...

if (!aBoolTest && (aTest == "++" || aTest == "--" || aTest == "**" || 
                aTest == "^/" || aTest == "/>" || aTest == "/<" || 
                aTest == "</=" || aTest == ">/=" || aTest == "/=") && aDoubleTest == .75)

Wouldn't it be nice if that could be written as something like...

if(!aBoolTest && aTest.IN("++","--",^/","/>","/<","</=",">/=","/=") && aDoubleTest == .75)

Using the Code

Well, in the first attempt in this article, I went completely in the wrong direction. See the comments prior to 13 May 2014 for far better solutions than my original. I guess my mind was still caught up thinking of my old VB6 solution!

However, the solution I was really after is even simpler in the context I'm using it ... to replace all those Ors. You just need an array of the values you are interested in - I've created the array on-the-fly within the if-statement itself - and the thing you're testing for. Then utilize the Contains method of the array. All you have to do is ensure that the array you create is the same type as the object you are testing against.

if (new string[] {"++", "--", "**", "^/", "/>", "/<", "/=", "/="}.Contains(aTest) )
    Debug.Print("Passed");  // Actions when test passes
else
    Debug.Print("Failed");  // Actions when test fails

If (New Char() {"+", "-", "*", "^", "/", "<", "=", ">"}).Contains(aCharTest) Then
    Debug.Print("Passed")   'Actions when test passes
Else
    Debug.Print("Failed")   'Actions when test fails
End If

Points of Interest

I did actually learn something while I was putting together this tip. VB.NET is not my language of choice, but I thought it would make sense to include the VB version here. I got a bit frustrated trying to create a static class in VB before realizing that I should have been using a Module to get that effect. Of course, now I'm not using either.

But now, I have another list of things to study further - namely extension methods and generics. So I got something out of this first time around, and will gain even more over the next few days courtesy of the members that commented to version 1.

To be honest, this still probably isn't the most original of ideas, and I still haven't seen anything like this documented. Still happy to stand corrected if I'm wrong.

History

• Version #1 - 12^th May, 2014
• Version #2 - 13^th May, 2014 - Changed approach to in-line array. Dropped the classes altogether
• Version #3 - 10^th March, 2017 - Fixed the formatting