From: bors <bors@rust-lang.org>
Date: Fri, 29 Jun 2018 04:09:02 +0000 (+0000)
Subject: Auto merge of #50357 - seanmonstar:arc-weak-null, r=KodrAus
X-Git-Url: https://git.lizzy.rs/?a=commitdiff_plain;h=3b50455c61847c4a417b5fb002a5258dbaf4a868;p=rust.git

Auto merge of #50357 - seanmonstar:arc-weak-null, r=KodrAus

Arc: remove unused allocation from Weak::new()

It seems non-obvious that calling `Weak::new()` actually allocates space for the entire size of `T`, even though you can **never** access that data from such a constructed weak pointer. Besides that, if someone were to create many `Weak:new()`s, they could be unknowingly wasting a bunch of memory.

This change makes it so that `Weak::new()` allocates no memory at all. Instead, it is created with a null pointer. The only things done with a `Weak` are trying to upgrade, cloning, and dropping, meaning there are very few places that the code actually needs to check if the pointer is null.
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3b50455c61847c4a417b5fb002a5258dbaf4a868