for vs foreach
You may think this is a superfluous post as there are many posts on web already discussing about performance measures when using for or foreach. Some of them are:
- For vs Foreach on arrays and list.
- For vs Foreach Performance.
- Which loop is faster for or foreach.
- and many more…
I would like to discuss something else here than that of performance measure. Recently while doing a peer code review I found following code snippet as a solution:
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I was just wondering what this code doing for a while. Initially only optimization I could think of was to avoid executing ++secondIndex once if expression is true i.e. secondIndex will always be larger for subsequent iterations. Just after few seconds wake up signal was sent to my mind and I said, ah – this is wrong! There is another hidden loop here which is nothing but a call to IndexOf. It is a linear search over the collection and time complexity of the algorithm is O(n). Using for loop here will be much faster and much more readable.
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Conclusion is that never use foreach when code inside loop have to deal with indexes.
