ocaml - String blit fails with error: This expression has type string but an expression was expected of type bytes

Question

While trying to compile the following expression :

String.blit (String.make tfs.len ' ') 0 tfs.txt 0 tfs.len;

the compiler complains with the following error :

Error: This expression has type string but an expression was expected of type bytes
and the variable 'tfs.txt' (of type string) is pointed at.

As suggested in some forum, I tried to set the variable OCAMLPARAM to the value: safe_string=0,_ but with no result

I'm using OCaml 4.11.1 under Ubuntu 20.01.01 LTS

Answer 1

Since OCaml 4.10.0, the distinction between immutable string and mutable bytes is a configure-time default that cannot be changed on a program-by-program basis.

If you are trying to compile some old legacy code, it might make sense to use a version of OCaml configured without this distinction.

Otherwise, it would be more future-proof to adapt your code to use bytes when in-place mutation of strings is needed (which is not clear from your code snippet).