Refinement of paragraph referenced by [this issue](https://github.com/rust-lang/rust/issues/31927).
The paragraph in question had been adjusted already, but I've made some further clarifications which should help with readability and not leave the reader any `dangling pointers`.
As a Rust newbie, I found the book's explanation for why the `filter` closure gets a reference very confusing, and tried to figure out why `filter` is somehow less consumptive than `map` -- but it isn't; that's controlled by `iter`/`into_iter`. I flailed around for a while until @habnabit explained it to me, and in retrospect it is quite obvious :-)
Reference implied that use declarations may appear *only* at the top of blocks and modules, but it is not the case, and the following is valid:
```Rust
fn foo() {
let x = 92;
use baz::bar;
}
```
r? @steveklabnik
I feel sorry for bothering you with such a literally one character changes. If it is counter productive feel free to point it out in the comments, that would be totally understandable. I could try to pack such a changes together in one PR to make them less distractive.
r? @steveklabnik
Not everyone knows this convention. We could just rename the variables in the
example, but since this notation is commonly used it's a good opportunity to
introduce it.
r? @steveklabnik
This is a minor change. Please see title. IMO this is important since this is the first instance when we talk about allocating a vector. Not saying that it is allocated on the stack here leaves room for speculation and this might put off some people (they might not even read the later sections which go into more detail about this).
The scope of these refactorings is a little bit bigger than the title implies. See each commit for details.
I’m submitting this for nitpicking now (the first 4 commits), because I feel the basic idea/implementation is sound and should work. I will eventually expand this PR to cover the translator changes necessary for all this to work (+ tests), ~~and perhaps implement a dynamic dropping scheme while I’m at it as well.~~
r? @nikomatsakis
