How does foreach loop work in c# i-e MSIL?

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How do foreach loops work in C#?

Just like classic iterative statments like for, while or do-while, is foreach loop is a new loop statment in c#? or in other languages such as php

OR

behind the scenes it translate our code to for, while or do-while loop.

What do you mean with "behind the scenes"? Are you talking about what MSIL looks like? — Candide, Jul 03 '12 at 18:07
Yes, it get's translated, but not to a native loop. See [iterators](http://en.wikipedia.org/wiki/Iterator). And in fact, it uses some kind of duck typing -- it only requires the iterated object to have a method `GetEnumerator`. — phipsgabler, Jul 03 '12 at 18:12

score 8 · Accepted Answer · answered Jul 03 '12 at 18:06

8

The foreach construction is equivalent to:

IEnumerator enumerator = myCollection.GetEnumerator();
try
{
   while (enumerator.MoveNext())
   {
       object current = enumerator.Current;
       Console.WriteLine(current);
   }
}
finally
{
   IDisposable e = enumerator as IDisposable;
   if (e != null)
   {
       e.Dispose();
   }
}

Note that this version is the non generic one. The compiler can handle IEnumerator<T>.

answered Jul 03 '12 at 18:06

Romain Verdier

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It also has some casts in there on the line where `current` is assigned. – Servy Jul 03 '12 at 18:11

Nikhil Agrawal · Answer 2 · 2012-07-03T18:12:51.560

4

Its not a new loop. Its been around since beginning.

The foreach statement repeats a group of embedded statements for each element in an array or an object collection. The foreach statement is used to iterate through the collection to get the desired information, but should not be used to change the contents of the collection to avoid unpredictable side effects.

class ForEachTest
{
    static void Main(string[] args)
    {
        int[] fibarray = new int[] { 0, 1, 2, 3, 5, 8, 13 };

        foreach (int i in fibarray)
            System.Console.WriteLine(i);
    }

}

Output

Unlike for loop which is used for index and accessing value like array[index], foreach works directly on value.

More here

edited Jul 03 '12 at 18:12

answered Jul 03 '12 at 18:04

Nikhil Agrawal

47,018
22
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It wasn't in the 1.x versions? Strange... – Austin Salonen Jul 03 '12 at 18:06
3

That's not correct. It's been there since the beginning. Here's a link to the 1.x version of the ECMA language specification http://www.ecma-international.org/publications/files/ECMA-ST-WITHDRAWN/ECMA-334,%202nd%20edition,%20December%202002.pdf – Brian Rasmussen Jul 03 '12 at 18:10

score 0 · Answer 3 · answered Jul 03 '12 at 18:10

0

It is a while loop infact and it uses GetEnumerator() method of container, see http://msdn.microsoft.com/en-us/library/aa664754(v=vs.71).aspx for details.

For arrays it is optimized to use indexer.

answered Jul 03 '12 at 18:10

Alexey F

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How does foreach loop work in c# i-e MSIL?

3 Answers3