Thursday, June 08, 2017

C# 6 String Interpolation Does Not Concatenate

Well, I learned something new today that's slightly disappointing. I had thought that C# 6 string interpolation concatenated strings or perhaps used the StringBuilder or some such under the hood. It turns out it merely creates a good, old-fashioned String.Format statement out of it.

Given this source code:

The resulting IL (compiled) code is the following:

Note the following two statements:
ldstr       "A{0}C"
call        System.String.Format
These indicate that String.Format is being called with the familiar-looking format string "A{0}C".

To compile the C# code and create IL code, I used Joe Albahari's excellent LINQPad program.