Why is printf in F# so slow?

Question

I\'ve just been really surprised by how slow printf from F# is. I have a number of C# programs that process large data files and write out a number of CSV files. I originall

Answer 1

I am not sure how much it matters, but...

Inspecting the code for printf:

https://github.com/fsharp/fsharp/blob/master/src/fsharp/FSharp.Core/printf.fs

I see

// The general technique used this file is to interpret
// a format string and use reflection to construct a function value that matches
// the specification of the format string.  

and I think the word 'reflection' probably answers the question.

printf is great for writing simple type-safe output, but if you want good perf in an inner loop, you might want to use a lower-level .NET API to write output. I haven't done my own benchmarking to see.