>>>I'd insert "in a loop" after strings, as they did some optimizatons for concatenating in a line and probably in directly following lines.
>>
>>As to 'and probably in directly following lines' I don't think so
>
>I've seen lines like

var stringres;
>stringres = str1 + str2 + str3;

>being described as special case where string concatenation is optimised.

Yes, I remember looking at that some time ago and I posted the results here

Up the 4 args and you get a call tho String.Concat( 2 to 4 args overload)

More than 4 - an array of string[] is created putting each arg into the array
Then String.Concat( string[] ) gets called

http://msdn.microsoft.com/en-us/library/System.String.Concat.aspx


>I'd expect

var stringres;
>stringres = "";
>stringres = stringres + str1;
>stringres = stringres + str2;
>stringres = stringres + str3;

>to be rewritten to form 1 by an optimizing compiler as such code can be found - if they can inline whole functions, inlining concats should be easy

No, I had checked before replying

Ildasm shows three calls to String.Concat(string, string)