Question

In Visual Studio Re-Sharper keeps recommending I convert a for loop to a linq expression but what is the reason for this?

Which is faster?

Here are some example loops where resharper suggests a linq conversion:

foreach (XmlNode legendEntryNode in _legendEntryNodes)
{
    var xmlElement = legendEntryNode["FeatureType"];

    if (xmlElement == null || !xmlElement.InnerText.Equals(featuretype)) continue;

    var xmlNodeList = legendEntryNode.SelectNodes("Themes/Theme");

    if (xmlNodeList != null)

    foreach (XmlNode themeNode in xmlNodeList)
    {
        var element = themeNode["Value"];

        if (element == null || !element.InnerText.Equals(v)) continue;

        var xmlElement1 = themeNode["Icon"];

        if (xmlElement1 != null)
        {
            string iconname = "<ms:ICON>" + xmlElement1.InnerText + "</ms:ICON>";

            var element1 = themeNode["Highlight"];

            if (element1 != null)
            {
                string highlightname = "<ms:HIGHLIGHT>" + element1.InnerText + "</ms:HIGHLIGHT>";
                gml = gml.Insert(c, iconname + highlightname);

                c += (iconname.Length + highlightname.Length);
            }
        }
        break;
    }
}

And this simpler example:

for (int i = 0; i < getPointsRequest.Attribs.Length; i++)
{
    string attribName = getPointsRequest.Attribs[i].AttributeName;

    if (!String.IsNullOrEmpty(attribName))
    {
        sqlQuery += "<ms:" + attribName + ">||\"" + attribName + "\"||</ms:" + attribName + ">";
    }
}

Answer 1

Speed is very often irrelevant in large portions of your code – you should write code the simplest way, and then measure it to make sure it’s fast enough.

If your for loop is really just querying, then LINQ is absolutely a great way to end up with more readable code. It’s not universally applicable, but it’s something you should at least bear in mind frequently.

Quite often a for loop can be converted into a query to be evaluated lazily, and then a foreach loop which performs some action on each value returned by the query. That can help separate the two aspects, letting you focus on one at a time when reading the code. It’s important to keep LINQ queries as queries though, rather than using side-effects within them – it’s designed to have a functional approach, which really doesn’t mix pleasantly with side-effects.

If you have some concrete examples, we could give more opinions about which loops would make sense to convert to use LINQ, and which wouldn’t.