std::iter: Introduce .by_ref() adaptor
Creates a wrapper around a mutable reference to the iterator.
This is useful to allow applying iterator adaptors while still
retaining ownership of the original iterator value.
Example::
let mut xs = range(0, 10);
// sum the first five values
let partial_sum = xs.by_ref().take(5).fold(0, |a, b| a + b);
assert!(partial_sum == 10);
// xs.next() is now `5`
assert!(xs.next() == Some(5));
---
This adaptor requires the user to have good understanding of
iterators or what a particular adaptor does. There could be some
pitfalls here with the iterator protocol, it's mostly the same issues
as other places regarding what happens after the iterator
returns None for the first time.
There could also be other ways to achieve the same thing, for
example Implementing iterator on `&mut T` itself:
`impl <T: Iterator<..>> Iterator for &mut T` but that would only
lead to confusion I think.
It is simply defined as `f64` across every platform right now.
A use case hasn't been presented for a `float` type defined as the
highest precision floating point type implemented in hardware on the
platform. Performance-wise, using the smallest precision correct for the
use case greatly saves on cache space and allows for fitting more
numbers into SSE/AVX registers.
If there was a use case, this could be implemented as simply a type
alias or a struct thanks to `#[cfg(...)]`.
Closes#6592
The mailing list thread, for reference:
https://mail.mozilla.org/pipermail/rust-dev/2013-July/004632.html
Creates a wrapper around a mutable reference to the iterator.
This is useful to allow applying iterator adaptors while still
retaining ownership of the original iterator value.
Example::
let mut xs = range(0, 10);
// sum the first five values
let partial_sum = xs.by_ref().take(5).fold(0, |a, b| a + b);
assert!(partial_sum == 10);
// xs.next() is now `5`
assert!(xs.next() == Some(5));
The trait will keep the `Iterator` naming, but a more concise module
name makes using the free functions less verbose. The module will define
iterables in addition to iterators, as it deals with iteration in
general.
Change the former repetition::
for 5.times { }
to::
do 5.times { }
.times() cannot be broken with `break` or `return` anymore; for those
cases, use a numerical range loop instead.
I removed the `static-method-test.rs` test because it was heavily based
on `BaseIter` and there are plenty of other more complex uses of static
methods anyway.
