Quick Tip: Comparing a .NET string to multiple values


The Problem

Do you ever wish you could use the SQL IN operator in your C# code to make your conditional blocks more concise and your code easier to read?

Perhaps it’s just my persnickety nature, but I believe that line-wrapped conditional expressions like this are a code smell.

if (animal.Equals("Cow") ||
   animal.Equals("Horse") ||
   animal.Equals("Hen"))
{
   Console.WriteLine("We must be on the farm.");
}

This would be so much cleaner…

if (animal.CompareMultiple("Cow","Horse","Hen")
{
   Console.WriteLine("We must be on the farm.");
}

The Code

With a simple extension class you can upgrade your string classes to do this very thing.

Step 1: Create an extension class as demonstrated here.

C#

namespace extenders.strings
{
  public static class StringExtender {

    public static bool CompareMultiple(this string data, StringComparison compareType, params string[] compareValues) {
      foreach (string s in compareValues) {
        if (data.Equals(s, compareType)) {
          return true;
        }
      }
      return false;
   }
  }
}

VB.NET

Imports System.Runtime.CompilerServices

Namespace Extenders.Strings

  Public Module StringExtender

    <Extension()> _
    Public Function CompareMultiple(ByVal this As String, compareType As StringComparison, ParamArray compareValues As String()) As Boolean

       Dim s As String

       For Each s In compareValues
         If (this.Equals(s, compareType)) Then
            Return True
         End If
       Next s

       Return False
    End Function

  End Module

End Namespace

Step 2: Add a reference to the extension namespace and use it.

C#

using extenders.strings;

namespace MyProgram
{
  static class program {
    static void Main() {

      string foodItem = "Bacon";

      if (foodItem.CompareMultiple(StringComparison.CurrentCultureIgnoreCase, "bacon", "eggs", "biscuit")) {
         System.Console.WriteLine("Breakfast!");
      }
      else {
         System.Console.Write("Dinner");
      }

    }
  }
}

VB.NET

Imports StringExtenderExampleVB.Extenders.Strings

Module Program

  Sub Main()
    Dim foodItem As String = "Bacon"

    If (foodItem.CompareMultiple(System.StringComparison.CurrentCultureIgnoreCase, "bacon", "eggs", "biscuit")) Then
      System.Console.WriteLine("Breakfast!")
    Else
      System.Console.Write("Dinner")
    End If

    System.Console.ReadLine()
  End Sub

End Module
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