No, I wasn't suggesting that you could implement the same high-performance System.String in IL, especially considering the assembly language used. I was just sa

No, I wasn't suggesting that you could implement the same high-performance System.String in IL, especially considering the assembly language used. I was just saying that there are many other things that can't be done in C# but are possible in .NET, using other languages. BTW there is a typo: "passed in my the calling code" should probably be "passed in by the calling code". I wonder if the new C# 6 string interpolation also uses string builder like format does. e.g. $"Name = {name}, hours = {hours:hh}" https://msdn.microsoft.com/en-us/library/Dn961160.aspx https://msdn.microsoft.com/en-us/library/Dn961160.aspx This post seems to suggest it uses concatenation, which may be bad for performance in some situations due to the immutability. https://weblogs.asp.net/bleroy/c-6-string-interpolation-is-not-a-templating-engine-and-it-s-not-the-new-string-format https://weblogs.asp.net/bleroy/c-6-string-interpolation-is-n...