Implement placement-in protocol for LinkedList

[apasel422]

CC #30172.

r? @pnkfelix
CC @nagisa

[pnkfelix]

I am not a member of the libs team, but my intuition is that the name emplace_back is longer than necessary; we don't have to follow C++'s precedent here.

Unfortunately deciding on a name for such methods does imply a bikeshedding discussion. . .

[pnkfelix]

Cc @rust-lang/libs

[apasel422]

@pnkfelix Agreed. Unfortunately, front and back are already taken.

[petrochenkov]

place(index), front(), back()	when front and back are not taken
place(index), front_place(), back_place()	when front and back are taken

[alexcrichton]

From a library API perspective this seems fine to me for now, we'll likely want to do a sweeping audit whenever we consider this for stabilization (aligning names for example), but for now having this as unstable seems fine to me!

[apasel422]

@alexcrichton So should I update any of the names for now?

[alexcrichton]

Oh I guess we don't have any prior art here (sorry I thought we had these implemented for vectors).

In terms of naming, we'll probably want to have a convention like iterators where it's super straightforward and you don't have to think about it much. Along those lines maybe something like:

• All "placer" methods have some shared word in them. Perhaps place or emplace (I don't have much of an opinion either way)
• Each collection may have a suite of placer methods, and if so they've all got some other prefix/suffix indicating how the placement is happening. Again, on whether it's a prefix/suffix I don't have much of an opinion
• The returned struct has the exact same name as the method, but in camel case

So I guess within those guidelines, I'd recommend renaming the returned structs, and otherwise keeping the names as is or the front_place/back_place suggestions @petrochenkov mentioned.

[apasel422]

Updated.

[pnkfelix]

@bors r+

[bors]

📌 Commit 895ab4f has been approved by pnkfelix

[bors]

⌛ Testing commit 895ab4f with merge b54770c...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-mac-ios-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt