Feature request: support opam switch -

[craigfe]

In interacting with Opam switches, I quite often find myself wanting to switch to a particular switch in order to perform a specific thing, then switch back to the switch I was on before:

$ opam switch plugin-host
$ ...                     # rebuild an opam plugin
$ opam switch irmin+4.10  # resume normal operation

The Git CLI has an idiom for this w.r.t branches, allowing git switch -:

$ git switch plugin-host
$ ...
$ git switch -             # go back to branch before `plugin-host`

(In fact, Git has a more general @{-N} syntax for referencing historic branch states, and - is a synonym of @{-1}.)

It might be nice if the opam CLI could support a similar syntax, although this would likely be a breaking change as it's currently possible to name an Opam switch "-".

[AltGr]

Indeed that could be convenient, it just means we would need to store a list of previously selected switches in the config.

For now, and for simple commands I'd just use --switch plugin-host for the intermediate commands :)