(Why) is invoking as extension method the preferred...way?

Question

I am in the process of resharpening my solution, using the just-released version of Resharper (2016.2.2)

It flags this line of code:

ReportRunnerConstsAndUtils.ConvertValueToAppropriateTypeAndAssign(totalPackagesCell, packages);

...intimating that I should "Invoke as extension method"

If I acquiesce, it changes that line to this:

totalPackagesCell.ConvertValueToAppropriateTypeAndAssign(packages);

Is this better? If so, how? why?

Here is the method being called, which is in a "ConstsAndUtils" class:

// Adapted from https://stackoverflow.com/questions/26483496/is-it-possible-to-ignore-excel-warnings-when-generating-spreadsheets-using-epplu
public static void ConvertValueToAppropriateTypeAndAssign(this ExcelRangeBase range, object value)
{
    string strVal = value.ToString();
    if (!String.IsNullOrEmpty(strVal))
    {
        decimal decVal;
        double dVal;
        int iVal;

        if (decimal.TryParse(strVal, out decVal))
            range.Value = decVal;
        if (double.TryParse(strVal, out dVal))
            range.Value = dVal;
        else if (Int32.TryParse(strVal, out iVal))
            range.Value = iVal;
        else
            range.Value = strVal;
    }
    else
        range.Value = null;
}

Answer 1

As some of the comments have indicated, this is at least partially a preference issue. Personally, I think it's "cleaner" and clearer to use an extension method here but some people may disagree with this.

"Under the hood," of course, the extension method is a static method (not an actual instance method), it's just that the compiler's giving you some syntactic sugar here (but that's besides the point).

Answer 2

It's recommended that you invoke it as an extension method, because you (or someone) CREATED it as an extension method. The syntax this ExcelRangeBase range makes that method an extension method, and so for consistencies sake, it should be used as an extension method when it is invoked. Otherwise you have lines that read ReportRunnerConstAndUtils.ConvertValueToAppropriateTypeAndAssign(range) and lines that do the exact same thing that read range.ConvertValueToAppropriateTypeAndAssign().

C#6 introduced some new syntax, and now you can have using ReportRunnerConstAndUtils at the top of you file and then ConvertValueToAppropriateTypeAndAssign(range) at your call site.