Forward more ExactSizeIterator methods and is_empty edits
#38149
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r? @sfackler (rust_highfive has picked a reviewer for you, use r? to override) |
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Huh, I don't understand this travis error, which shows up in tidy after it already built the regular build successfully. error: unused or unknown feature
--> /checkout/src/liballoc/lib.rs:82:12
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82 | #![feature(exact_size_is_empty)]
| ^^^^^^^^^^^^^^^^^^^
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Improve is_empty on the VecDeque and its iterators by just comparing tail and head; this saves a few instructions (to be able to remove the `& (size - 1)` computation, it would have to know that size is a power of two).
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I've tried to address the tidy failure by making the exact_size_is_empty feature conditional; it's unused when |
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@bors: r+ Thanks! |
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📌 Commit d53f82c has been approved by |
bors
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Dec 7, 2016
Forward more ExactSizeIterator methods and `is_empty` edits - Forward ExactSizeIterator methods in more places, like `&mut I` and `Box<I>` iterator impls. - Improve `VecDeque::is_empty` itself (see commit 4) - All the collections iterators now have `len` or `is_empty` forwarded if doing so is a benefit. In the remaining cases, they already use a simple size hint (using something like a stored `usize` value), which is sufficient for the default implementation of len and is_empty.
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&mut IandBox<I>iterator impls.VecDeque::is_emptyitself (see commit 4)lenoris_emptyforwarded if doing so is a benefit. In the remaining cases, they already use a simple size hint (using something like a storedusizevalue), which is sufficient for the default implementation of len and is_empty.