Move treemap libextra to libstd

[recrack]

#10275

Thanks to @brson

[brson]

Do we know what the tradeoffs between HashMap and TreeMap are? What's the benefit of having both?

[brson]

Thanks @recrack!

[thestinger]

@brson: TreeMap is an ordered map so you can iterate over the keys in-order or do fast range searches. The cost is that the operations are O(log n) (search) or amortized O(log n) instead of an O(1) average case (which with SipHash is a fairly strong guarantee if the universe doesn't hate you).

If we do get a nice B-tree implementation, it would likely make sense to replace this red-black tree implementation with it but the API would remain the same.

[brson]

@recrack Can you remove the second commit that ignores the memory map test? I'm not sure what's happening on your machine but the bots aren't seeing that error.

[brson]

@thestinger Thanks.

[recrack]

Thanks @brson @thestinger
I removed second commit.

[chris-morgan]

The failure is genuine: when running tests, only that crate will be built with #[cfg(test)], so moving the test-only mod extra::containers::bench to std has broken extra tests, because it only has a non-test std.

[alexcrichton]

Closing due to inactivity, but feel free to reopen with updates!