String Interpolation vs String.Format

Question

Is there a noticable performance difference between using string interpolation:

myString += $"{x:x2}";

vs String.Format()?

myString += String.Format("{0:x2}", x);

I am only asking because Resharper is prompting the fix, and I have been fooled before.

Answer 1

Noticable is relative. However: string interpolation is turned into string.Format() at compile-time so they should end up with the same result.

There are subtle differences though: as we can tell from this question, string concatenation in the format specifier results in an additional string.Concat() call.

Answer 2

string interpolation is turned into string.Format() at compile-time.

Also in string.Format you can specify several outputs for single argument, and different output formats for single argument. But string interpolation is more readable I guess. So, it's up to you.

a = string.Format("Due date is {0:M/d/yy} at {0:h:mm}", someComplexObject.someObject.someProperty);

b = $"Due date is {someComplexObject.someObject.someProperty:M/d/yy} at {someComplexObject.someObject.someProperty:h:mm}";

There is some performance test results https://koukia.ca/string-interpolation-vs-string-format-string-concat-and-string-builder-performance-benchmarks-c1dad38032a