Auto merge of #34532 - jonmarkprice:master, r=steveklabnik

Book: Small grammatical and stylistic edits to book

I've been reading [the book](https://doc.rust-lang.org/book/) and noticed a few small grammatical and stylistic issues which I've rolled into this pull request.

I'm not sure if I should do so many small, unrelated edits in a single pull request but it seems like a lot of overhead for each small edit. Maybe one commit per edit but one pull request per file/section? Feedback is very much appreciated as this is my first pull request ever!

r? @steveklabnik rollup

src/doc/book/lifetimes.md

@@ -290,7 +290,7 @@ lifetime parameters using three easily memorizable and unambiguous rules. This m
 acts as a shorthand for writing an item signature, while not hiding
 away the actual types involved as full local inference would if applied to it.
 
-When talking about lifetime elision, we use the term *input lifetime* and
+When talking about lifetime elision, we use the terms *input lifetime* and
 *output lifetime*. An *input lifetime* is a lifetime associated with a parameter
 of a function, and an *output lifetime* is a lifetime associated with the return
 value of a function. For example, this function has an input lifetime:
@@ -335,11 +335,13 @@ fn print<'a>(s: &'a str); // expanded
 
 fn debug(lvl: u32, s: &str); // elided
 fn debug<'a>(lvl: u32, s: &'a str); // expanded
+```
 
-// In the preceding example, `lvl` doesn’t need a lifetime because it’s not a
-// reference (`&`). Only things relating to references (such as a `struct`
-// which contains a reference) need lifetimes.
+In the preceding example, `lvl` doesn’t need a lifetime because it’s not a
+reference (`&`). Only things relating to references (such as a `struct`
+which contains a reference) need lifetimes.
 
+```rust,ignore
 fn substr(s: &str, until: u32) -> &str; // elided
 fn substr<'a>(s: &'a str, until: u32) -> &'a str; // expanded
 

src/doc/book/ownership.md

@@ -214,7 +214,7 @@ But, unlike a move, we can still use `v` afterward. This is because an `i32`
 has no pointers to data somewhere else, copying it is a full copy.
 
 All primitive types implement the `Copy` trait and their ownership is
-therefore not moved like one would assume, following the ´ownership rules´.
+therefore not moved like one would assume, following the ‘ownership rules’.
 To give an example, the two following snippets of code only compile because the
 `i32` and `bool` types implement the `Copy` trait.
 
@@ -290,6 +290,6 @@ let (v1, v2, answer) = foo(v1, v2);
 Ugh! The return type, return line, and calling the function gets way more
 complicated.
 
-Luckily, Rust offers a feature, borrowing, which helps us solve this problem.
-It’s the topic of the next section!
+Luckily, Rust offers a feature which helps us solve this problem.
+It’s called borrowing and is the topic of the next section!
 

src/doc/book/references-and-borrowing.md

@@ -123,7 +123,7 @@ let v = vec![];
 foo(&v);
 ```
 
-errors with:
+will give us this error:
 
 ```text
 error: cannot borrow immutable borrowed content `*v` as mutable
@@ -152,8 +152,8 @@ the thing `y` points at. You’ll notice that `x` had to be marked `mut` as well
 If it wasn’t, we couldn’t take a mutable borrow to an immutable value.
 
 You'll also notice we added an asterisk (`*`) in front of `y`, making it `*y`,
-this is because `y` is a `&mut` reference. You'll also need to use them for
-accessing the contents of a reference as well.
+this is because `y` is a `&mut` reference. You'll need to use astrisks to
+access the contents of a reference as well.
 
 Otherwise, `&mut` references are like references. There _is_ a large
 difference between the two, and how they interact, though. You can tell
@@ -179,7 +179,7 @@ As it turns out, there are rules.
 
 # The Rules
 
-Here’s the rules about borrowing in Rust:
+Here are the rules for borrowing in Rust:
 
 First, any borrow must last for a scope no greater than that of the owner.
 Second, you may have one or the other of these two kinds of borrows, but not
@@ -208,12 +208,14 @@ With this in mind, let’s consider our example again.
 Here’s the code:
 
 ```rust,ignore
-let mut x = 5;
-let y = &mut x;
+fn main() {
+    let mut x = 5;
+    let y = &mut x;
 
-*y += 1;
+    *y += 1;
 
-println!("{}", x);
+    println!("{}", x);
+}
 ```
 
 This code gives us this error:
@@ -225,7 +227,7 @@ error: cannot borrow `x` as immutable because it is also borrowed as mutable
 ```
 
 This is because we’ve violated the rules: we have a `&mut T` pointing to `x`,
-and so we aren’t allowed to create any `&T`s. One or the other. The note
+and so we aren’t allowed to create any `&T`s. It's one or the other. The note
 hints at how to think about this problem:
 
 ```text
@@ -243,14 +245,16 @@ In Rust, borrowing is tied to the scope that the borrow is valid for. And our
 scopes look like this:
 
 ```rust,ignore
-let mut x = 5;
-
-let y = &mut x;    // -+ &mut borrow of x starts here
-                   //  |
-*y += 1;           //  |
-                   //  |
-println!("{}", x); // -+ - try to borrow x here
-                   // -+ &mut borrow of x ends here
+fn main() {
+    let mut x = 5;
+
+    let y = &mut x;    // -+ &mut borrow of x starts here
+                       //  |
+    *y += 1;           //  |
+                       //  |
+    println!("{}", x); // -+ - try to borrow x here
+}                      // -+ &mut borrow of x ends here
+                       
 ```
 
 The scopes conflict: we can’t make an `&x` while `y` is in scope.
@@ -269,12 +273,12 @@ println!("{}", x);  // <- try to borrow x here
 ```
 
 There’s no problem. Our mutable borrow goes out of scope before we create an
-immutable one. But scope is the key to seeing how long a borrow lasts for.
+immutable one. So scope is the key to seeing how long a borrow lasts for.
 
 ## Issues borrowing prevents
 
 Why have these restrictive rules? Well, as we noted, these rules prevent data
-races. What kinds of issues do data races cause? Here’s a few.
+races. What kinds of issues do data races cause? Here are a few.
 
 ### Iterator invalidation
 
@@ -323,7 +327,7 @@ for i in &v {
 
 We can’t modify `v` because it’s borrowed by the loop.
 
-### use after free
+### Use after free
 
 References must not live longer than the resource they refer to. Rust will
 check the scopes of your references to ensure that this is true.