RFC to remove some special treatment of Box by borrow checker by nikomatsakis · Pull Request #130 · rust-lang/rfcs (original) (raw)

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nikomatsakis

@nikomatsakis

@anasazi

I don't understand the motivation for doing this (but then I've never understood the obsession everyone else has with treating unique pointers just like non-unique pointers) especially when the proposed design still special cases Box so that moves out are allowed.

I really just don't understand why we would want to make our type system more restrictive just because we can exploit information about Box that we can't about smart pointers. Seems like it would be going backward.

@zwarich

As discussed in this week's Rust meeting, I went ahead and implemented this change to see what the fallout would be like. There are only two changes required in the Rust distribution (I'm not including tests, since they are designed to test all of the edge cases):

https://gist.github.com/zwarich/348d5726d1ef42f109ee

I'll finish going through tests and double-check that I implemented everything correctly, but this looks like minimal impact on any real-world code.

@zwarich

@anasazi We can remove the special-casing for moves out of Box by doing something like #178. It doesn't appear to be possible to do the same thing in a safe fashion for the special cases discussed in this RFC.

@zwarich

@brson brson mentioned this pull request

Jul 30, 2014

@brson

withoutboats pushed a commit to withoutboats/rfcs that referenced this pull request

Jan 15, 2017

@alexcrichton

Fix links to tokio-tls documentation

@pnkfelix

At some point we should document the fact that NLL has gone back to adding (more) special treatment of Box<T>. One big reason we were able to justify this is that we discovered several more instances where AST-borrowck was also special casing its treatment of Box<T>, so it was more consistent overall to just special case Box<T> consistently within NLL.

@pnkfelix

See e.g. this snippet of conversation regarding the special treatment of Box (which was originally a concern blocking NLL from moving forward): rust-lang/rust#43234 (comment)

pietroalbini added a commit to pietroalbini/rust that referenced this pull request

Nov 10, 2018

@pietroalbini

…est-for-nll, r=davidtwco

NLL: Update box insensitivity test

This is just keeping one of our tests honest with respect to NLL, in two ways:

  1. Adds uses of borrows that would otherwise be too short to observe the error that we would have expected to see...
  2. ... I say "would have expected" because all of the errors in this file are part of the reversion of rust-lang/rfcs#130 that is attached to NLL (you can see more discussion of this here rust-lang#43234 (comment) )