Thursday, March 30, 2017

C# String Interpolation Performance

Time for a follow up to my String.Concat vs String.Format Performance post from back in 2014!

I recently found out that string interpolation is not nearly as efficient as I would have thought. I also suspected that it was just doing a string concatenation, but it is actually doing a string format. This leads to a pretty significant performance degradation; the following test runs one million iterations of each.

Number
of Args
Interpolation
Milliseconds
String.Format
Milliseconds
String.Concat
Milliseconds
String Add
Milliseconds
StringBuilder
Milliseconds
2 262 260 19 18 34
3 367 367 25 24 35
4 500 513 31 32 41
5 646 635 67 66 44
6 740 723 79 76 49
7 802 819 86 85 52
8 938 936 97 98 58

So, what's the lesson? Don't use string interpolation in high performance areas (such as your logger)!

Enjoy,
Tom

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