Implement placement-in protocol for relevant data structures

[nagisa]

We currently have the unstable new arrow syntax (<-) for placement-in in nightly with intention to see how people like the syntax/how ergonomic it is/etc. However, it is pretty hard to try the syntax out without having any useful/common data-structures implementing the placement-in protocol and thus it is pretty unlikely for us to collect much feedback on the syntax.

The Placer, Place and InPlace traits should be implemented for following data structures as appropriate:

• Vec (&mut myvec <- value; see this RFC regarding mutable reference) Implement placement-in protocol for Vec #32366
• HashMap through Entry (i.e. mymap.entry(k) <- value) Implement placement-in protocol for HashMap #40390
• BTreeMap through Entry.
• LinkedList Implement placement-in protocol for LinkedList #31696
• BinaryHeap (&mut heap <- value) Implement placement-in protocol for BinaryHeap #39062
• VecDeque (front_place and back_place, like LinkedList) Implement placement-in protocol for VecDeque #40389

It should also be investigated how viable implementing placement protocol is for other std::collections collections and possibly implementing these as well.

Since both placement protocol and placement-in syntax are unstable, there’s no stability hazard.

cc @pnkfelix.

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I personally feel this issue has tons of potential to help people get acquainted with rust’s standard library (i.e. is in E-easy land) and would be willing to answer any questions (E-mentor) regarding implementation strategies on IRC or the issue itself.

[pnkfelix]

we might consider myvec.back() <- value; rather than myvec <- value;. the main reason I can think of of hand is that there may be issues related to indexing sugars, e.g. ambiguity of mymap[k] <- value; when you have a map with vec values.

[apasel422]

@nagisa BTreeMap is also a candidate through its Entry.

[nagisa]

@apasel422 added to the list.

[nagisa]

Since the LinkedList has been implemented one could use the PR as example when implementing the protocol for other collections.

[notmatt]

@nagisa this looks like something I'd like to take a swing at; would some initial code in a week (±a weekend) be ok?

[nagisa]

Sure!
On Feb 18, 2016 10:12 PM, "Matthew Smillie" notifications@github.com
wrote:

@nagisa https://github.com/nagisa this looks like something I'd like to
take a swing at; would some initial code in a week (±a weekend) be ok?

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Reply to this email directly or view it on GitHub
#30172 (comment).

[notmatt]

@nagisa quick update: apart from an unexpected shortage of spare time, this is going well. I've mostly been reading/understanding Placer et alia & the LinkedList implmentation. I'm starting with the VecDeque given its broad similarity, but not a lot to show yet.