Re: concat with separators ?

[Tino Calancha]

On Sun, 28 May 2017, Jean-Christophe Helary wrote:

> > On May 28, 2017, at 19:52, Tino Calancha <address@hidden> wrote:
> >
> > > > > That's roughly the definition of string-join in subr-x:
> > > > >
> > > > > (defsubst string-join (strings &optional separator)
> > > > > "Join all STRINGS using SEPARATOR."
> > > > > (mapconcat 'identity strings separator))
> > >
> > > Would it be acceptable to provide separators to concat or is it preferable to 
> > > use string-join instead?
>
> > The latter.
> > Func. `concat' accepts any arbitrary number of sequences (not a list of
> > sequences as `string-join').
>
> I know that, but subr-x is experimental (hence not documented in the manual) 
> and having to use mapconcat just to add a separator seems not practical.
I wouldn't worry too much about `string-join' not being in the manual. 
It's going to keep there.  If it's convenient for you feel free to use it.
Many people here like to use stuff from subr-x.el.

Or you can create in your package a `foo-string-join' (foo being your 
package prefix).  Once you write your package manual, this function will 
be documented in the Emacs manual as well.

We cannot modify `concat' with a new argument `separator' without breaking 
existent code.
You can pass the separator between strings:

(concat "foo" ":" "bar" ":" "qux")
=> "foo:bar:qux"

Or use format:
(format "%s:%s:%s" "foo" "bar" "qux")
=> "foo:bar:qux"