Implement Write for Cursor<&mut Vec<u8>>

[Diggsey]

Fixes #30132

r? @dtolnay (I'm just going through feature-accepted issues I swear 😛)

[kennytm]

Thanks for the PR! We’ll periodically check in on it to make sure that @dtolnay or someone else from the team reviews it soon.

[dtolnay]

Thanks! The implementation looks good to me. Let's run it by the rest of the libs team though.

[dtolnay]

@rust-lang/libs this adds the following impl. This is important for being able to write to a Vec owned by a Mutex or similar.

impl<'a> Write for Cursor<&'a mut Vec<u8>>

@rfcbot fcp merge

[rfcbot]

Team member @dtolnay has proposed to merge this. The next step is review by the rest of the tagged teams:

• @BurntSushi
• @Kimundi
• @alexcrichton
• @aturon
• @dtolnay
• @sfackler

No concerns currently listed.

Once these reviewers reach consensus, this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[alexcrichton]

@bors: r+

[bors]

📌 Commit 77b3090 has been approved by alexcrichton

[bors]

⌛ Testing commit 77b3090 with merge 27ede55...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 27ede55 to master...

[est31]

Thank you @Diggsey !

[oconnor663]

We might want to tweak the title here to replace T with u8, since this PR gets linked to by some recent announcements.

[clouds56]

Should we mention the behavior of resize in the document? (otherwise one might not sure if Cursor<&mut Vec<u8>> would do the same as Cursor<&mut [u8]>)

Cursors are used with in-memory buffers, anything implementing AsRef<[u8]>, to allow them to implement Read and/or Write, allowing these buffers to be used anywhere you might use a reader or writer that does actual I/O. the buffer of Cursor<&mut [u8]> would not be increased when the space runs out while Cursor<Vec<u8>> and Cursor<&mut Vec<u8>> would just like an actual file.

I'd like to provide File-like in-memory buffer to some API accept W: Write, it takes me time to find out I could use Cursor<&mut Vec<u8>> before I see this PR.