[Caml-list] What is an unsafe feature?

[Caml-list] What is an unsafe feature?

[Hendrik Tews]

Hi,

I always thought that the Obj module is unsafe and that functions
containing "unsafe" in their name are unsafe too. However, when I
run ocamlobjinfo on the .cmo of

    let f b =
      let a = "abcde" in
      let c = Obj.magic b in
      String.unsafe_blit c 0 a 0 5

I see (with 3.12.1 and 4.00.1)

    Uses unsafe features: no

So what is considered unsafe by ocamlobjinfo?

For .cmx files, ocamlobjinfo says nothing about unsafe features.
Is this info not present in the .cmx?

Bye,

Hendrik

RE: [Caml-list] What is an unsafe feature?

[David Allsopp]

Hendrik Tews wrote:
> Hi,
> 
> I always thought that the Obj module is unsafe and that functions
> containing "unsafe" in their name are unsafe too. However, when I run
> ocamlobjinfo on the .cmo of
> 
>     let f b =
>       let a = "abcde" in
>       let c = Obj.magic b in
>       String.unsafe_blit c 0 a 0 5
> 
> I see (with 3.12.1 and 4.00.1)
> 
>     Uses unsafe features: no
> 
> So what is considered unsafe by ocamlobjinfo?

I think, looking at tools/objinfo.ml and tools/primreq.ml that this only refers to the compilation unit itself, not interfaces which it imports (try running ocamlobjinfo on stdlib.cma). The .cmo above simply imports Pervasives, String, Obj - the information that those are primitives is not recorded. If you changed it to:

external magic : 'a -> 'b = "%identity"
let f b =
  let a = "abcde" in
  let c = magic b in
  String.unsafe_blit c 0 a 0 5

Then you will see the unsafe features warning from ocamlobjinfo.


David