mozilla/rust — pull request #8527 by pnkfelix (2013-08-15 02:35:55+00:00)
Title: Visitor trait rewrite, step 1.

Rewriting visit.rs to operate on a borrowed `&mut V` where ``

r? @nikomatsakis
r? @pcwalton

This is the first in a planned series of incremental pull requests. (There will probably be five pull requests including this one, though they can be combined or split as necessary.)

Part of #7081. (But definitely does *not* complete it, not on its own, and not even after all five parts land; there are still a few loose ends to tie up or trim afterwards.)

The bulk of this change for this particular PR is pnkfelix@3d83010, which has the changes necessary to visit.rs to support everything else that comes later. The other commits are illustrating the standard mechanical transformation that I am applying.

One important point for nearly *all* of these pull requests: I was deliberately *not* trying to be intelligent in the transformation.

* My goal was to minimize code churn, and make the transformation as mechanical as possible.
* For example, I kept the separation between the Visitor struct (corresponding to the earlier vtable of functions that were potentially closed over local state) and the explicitly passed (and clones) visitor Env. I am certain that this is almost always unnecessary, and a later task will be to go through an meld the Env's into the Visitors as appropriate. (My original goal had been to make such melding part of this task; that's why I turned them into a (Env, vtable) tuple way back when. But I digress.)
* Also, my main goal here was to get rid of the record of `@fn`'s as described by the oldvisit.rs API. (This series gets rid of all but one such case; I'm still investigating that.) There is *still* plenty of `@`-boxing left to be removed, I'm sure, and even still some `@fn`'s too; removing all of those is not the goal here; its just to get rid of the encoded protocol of `@fn`'s in the (old)visit API.

To see where things will be going in the future (i.e., to get a sneak-preview of future pull-requests in the series), see:

* https://github.com/pnkfelix/rust/commits/fsk-visitor-vpar-defaults-step1 (that's this one)
* https://github.com/pnkfelix/rust/commits/fsk-visitor-vpar-defaults-step2
* https://github.com/pnkfelix/rust/commits/fsk-visitor-vpar-defaults-step3
* https://github.com/pnkfelix/rust/commits/fsk-visitor-vpar-defaults-step4
* https://github.com/pnkfelix/rust/commits/fsk-visitor-vpar-defaults-step5
* Note that between step 4 and step 5 there is just a single commit, but its a doozy because its the only case where my mechanical transformation did not apply, and thus more serious rewriting was necessary. See commit pnkfelix@da902b2ff3b1e0bee9fc63cf00c449cceea8abf7