Question

This is a simple question really (but I couldn’t seem to find the answer in the MSDN documents).

If I pass large sequences and objects as function parameters in F#, are they always copied by value unless I supply the byref keyword? The thing is, I have no intention of modifying the arguments, but at the same time, I don’t want the large objects to be copied each time I call the function.

Answer 1

By default sequences/lists/arrays are passed by reference

for example

let mutate (arr:int[]) =
    arr.[0] <- 1

let t = Array.zerocreate 1
mutate t
printfn "%i" (t.[0]) //prints 1