Is there a way to shorten the condition if it always compares to the same thing?

Question

I have always found it annoying when I need to write a condition that compares the same item over and over again since I would have the type the item so many times:

string x = textBox1.Text;

if (x == "apple" || x == "orange" || x == "banana" ...)
...

I want something like this (but of course this is not correct syntax):

if (x == "apple" || "orange" || "banana" ...)

Is there a solution other than using an array of the strings?

Answer 1

Your condition says: I'm true if I match any of the predefined values. In other words if I'm an element of a predefined set which is semantically the Contains method:

if (new [] { "apple", "orange", "banana" }.Contains(x))
{

}

Using an array provides much more flexibility in the future. You can extract it out, reuse it, store it, chache it etc. I always use "arrays and loops" when I have to deal with more than 2 known values.

Note: As Scott Chamberlain pointed out in the comments with using HashSet<T>.Contains greatly improves the performace:

var values = new HashSet<string> { "apple", "banana", "orange" };
if (values.Contains(x))
{

}

Answer 2

What about an extension method?

public static class Extensions
{
   public static bool IsOneOf<T>(this T input, params T[] possibilites)
   {
      bool result = possibilites.Contains(input);
      return result;
   }
}

You could then rewrite your code to look like this:

string input = textBox1.Text;
if(input.IsOneOf("apple", "orange", "banana"))
{
    // ....
}

Answer 3

You can move duplicated code to the method, which also will explain why this code is duplicated - because it verifies whether something is fruit. It will increase readability and maintainability of your code. Also you will be able to refactor this logic (e.g. turning it into switch statement):

private bool IsFruit(string name)
{
   switch(name)
   {
       case "apple":
       case "orange":
       ...
       case "banana":
           return true;
       default:
           return false;
   }
}

Usage:

string x = textBox1.Text;
if(IsFruit(x))
   ...

UPDATE: Better do not use such complex conditions - it's really hard to understand sometimes. You can use Introduce Explaining Variable or Extract Method (as above) refactorings to make your code more clear.

Answer 4

Your best bet (in terms of performance) is to use HashSet

    static HashSet<string> Fruits = new HashSet<string> {"apple", "banana", "orange"};

    string x = textBox1.Text;
    if( Fruits.Contains( x)) {

Once you get beyond three or so possibilities in the if condition, a HashSet will run faster than straight comparison.

Answer 5

linq solution

var strarray = new string[]
        {
            "apple",
            "orange",
            "banana"
        };

bool a = strarray.Any( x=> x ==  textBox1.Text);
if(a)
 //CODE 
else 
 //code

---

try switch case like this

Switch(value)
{
  case "apple":
  case "orange":
  case "banana":....
    //code you want
  break;
}

Answer 6

use a switch statement with like so

switch (x)
{
   case "apple":
   case "orange":
   case "banana":
      //code
      break;
}

Answer 7

You could try a switch statement:

switch (x)
{
    case "apple":
    case "orange":
    case "banana":
        //...
        break;
}

Answer 8

You can use a switch statement:

switch(x)
{
    case "apple":
    case "orange":
    case "banana":
        // "if" code goes here
        break;
    default:
        // "else" code goes here
        break;
}

Answer 9

I like the extension method solution and have used it before. Here are the methods I have available in my "CommonUtils" library:

    public static bool IsIn<T>(this T toFind, IEnumerable<T> collection)
    {
        return collection.Contains(toFind);
    }

    public static bool IsIn<T>(this T toFind, ICollection<T> collection)
    {
        return collection.Contains(toFind);
    }

    public static bool IsIn<T>(this T toFind, params T[] items)
    {
        return toFind.IsIn(items.AsEnumerable());
    }

Between these three, you can pretty much use any collection, and you can also specify the items as a parameter list.

Answer 10

You could do something like this:

string it = "apple,orange,banana";

if(it.Contains(x))
{
  //do work
}

Even simpler:

if("apple,orange,banana".Contains(x))
    {
      //do work
    }