String.sub throws Invalid_argument("Bytes.sub") "

[vicuna]

Original bug ID: 6557
Reporter: oliver
Status: closed (set by @xavierleroy on 2016-12-07T10:36:47Z)
Resolution: fixed
Priority: normal
Severity: minor
Platform: PC / Linux
OS: Arch Linux
Version: 4.02.0+beta1 / +rc1
Target version: 4.02.1+dev
Fixed in version: 4.02.1+dev
Category: standard library
Related to: #6560
Monitored by: @gasche @hcarty

Bug description

String.sub throws Invalid_argument("Bytes.sub") when non-valid susbstring found.

Steps to reproduce

In Toplevel:

String.sub;;

• : string -> int -> int -> string =

String.sub "" 0 1 ;;

Exception: Invalid_argument "Bytes.sub".

[vicuna]

Comment author: oliver

OCaml version 4.02.0

[vicuna]

Comment author: @gasche

So we have the following options:

A) do nothing
B) try..with (probably too slow)
C) use "String.sub" in the exception for both Bytes.sub and String.sub

The point that the string content of the exception is unspecified is fair, and (A) is therefore a valid choice. But it breaks user code; I'd rather be tempted to try (C). Any opinions?

[vicuna]

Comment author: @damiendoligez

I like (C), but we have similar problems with:

fill (which is deprecated)
blit (raises Bytes.blit_string)
index_from
rindex_from
contains_from
rcontains_from

[vicuna]

Comment author: @gasche

I'd vote for (C) on all of them.

[vicuna]

Comment author: @damiendoligez

Another possibility:

D) raise Invalid_argument "String.sub / Bytes.sub"

[vicuna]

Comment author: @damiendoligez

Fixed in branch 4.02 (commit 15520) with solution D. People who match on the string will have a bad surprise but we'll explain that they shouldn't do that.