Hi Will,

On Mon, 2018-08-27 at 13:12 +0930, Will Robertson wrote:
> If you really know that users will be updating/using new versions of
> your package on outdated systems, and they can’t/won't upgrade
> l3kernel itself, the best/easiest thing to do in this case would be
> to have code like:
> 
> \cs_if_exist:NF \ior_str_get:NN
>   { \cs_set_eq:NN \ior_str_get:NN \ior_get_str:NN }
> 
> (Perhaps with a warning in there that if at all possible the user
> should update their expl3 version.) And then use the updated version
> of the command.

Adding a warning sounds like a good idea.

Hmm, do you think that will work? I had tried the following[1]:

   \cs_if_exist:NF \ior_str_get:NN { \cs_new_eq:NN \ior_str_get:NN \ior_get_str:NN }

However, while this worked fine with older LaTeX distributions, the
user with a newer distribution reported the following error:

   Runaway argument?
   {\cs_new_eq:NN \ior_str_get:NN
   ! Forbidden control sequence found while scanning use of \use_i:nn.
   <inserted text>
   \par
   l.34 ..._new_eq:NN \ior_str_get:NN \ior_get_str:NN
   }

I have no idea why that error is happening here, it must have something
to do with the code to emit the deprecation warning.

Maybe \cs_set_eq:NN will behave better, I can try that later.

Regards,
Benjamin

[1] https://github.com/sdaps/sdaps-class/blob/master/sdapsarray.dtx#L125