Merge pull request #4121 from rust-lang/error-fixes-shadowing

Fix a couple inverted uses of “shadowed”

Author: chriskrycho

src/ch12-05-working-with-environment-variables.md

@@ -55,14 +55,14 @@ they’ll be the same case when we check whether the line contains the query.
 
 </Listing>
 
-First we lowercase the `query` string and store it in a shadowed variable with
-the same name. Calling `to_lowercase` on the query is necessary so that no
-matter whether the user’s query is `"rust"`, `"RUST"`, `"Rust"`, or `"rUsT"`,
-we’ll treat the query as if it were `"rust"` and be insensitive to the case.
-While `to_lowercase` will handle basic Unicode, it won’t be 100% accurate. If
-we were writing a real application, we’d want to do a bit more work here, but
-this section is about environment variables, not Unicode, so we’ll leave it at
-that here.
+First we lowercase the `query` string and store it in a new variable with the
+same name, shadowing the original. Calling `to_lowercase` on the query is
+necessary so that no matter whether the user’s query is `"rust"`, `"RUST"`,
+`"Rust"`, or `"rUsT"`, we’ll treat the query as if it were `"rust"` and be
+insensitive to the case. While `to_lowercase` will handle basic Unicode, it
+won’t be 100% accurate. If we were writing a real application, we’d want to do a
+bit more work here, but this section is about environment variables, not
+Unicode, so we’ll leave it at that here.
 
 Note that `query` is now a `String` rather than a string slice because calling
 `to_lowercase` creates new data rather than referencing existing data. Say the

src/ch19-01-all-the-places-for-patterns.md

@@ -82,13 +82,13 @@ This conditional structure lets us support complex requirements. With the
 hardcoded values we have here, this example will print `Using purple as the
 background color`.
 
-You can see that `if let` can also introduce shadowed variables in the same way
-that `match` arms can: the line `if let Ok(age) = age` introduces a new
-shadowed `age` variable that contains the value inside the `Ok` variant. This
-means we need to place the `if age > 30` condition within that block: we can’t
-combine these two conditions into `if let Ok(age) = age && age > 30`. The
-shadowed `age` we want to compare to 30 isn’t valid until the new scope starts
-with the curly bracket.
+You can see that `if let` can also introduce new variables which shadow existing
+variables in the same way that `match` arms can: the line `if let Ok(age) = age`
+introduces a new shadowed `age` variable that contains the value inside the `Ok`
+variant. This means we need to place the `if age > 30` condition within that
+block: we can’t combine these two conditions into `if let Ok(age) = age && age >
+30`. The shadowed `age` we want to compare to 30 isn’t valid until the new scope
+starts with the curly bracket.
 
 The downside of using `if let` expressions is that the compiler doesn’t check
 for exhaustiveness, whereas with `match` expressions it does. If we omitted the

src/ch19-03-pattern-syntax.md

@@ -29,7 +29,7 @@ value `Some(5)` and a variable `y` with the value `10`. We then create a
 `println!` at the end, and try to figure out what the code will print before
 running this code or reading further.
 
-<Listing number="19-11" file-name="src/main.rs" caption="A `match` expression with an arm that introduces a shadowed variable `y`">
+<Listing number="19-11" file-name="src/main.rs" caption="A `match` expression with an arm that introduces a new variable which shadows an existing variable `y`">
 
 ```rust
 {{#rustdoc_include ../listings/ch19-patterns-and-matching/listing-19-11/src/main.rs:here}}
@@ -60,10 +60,10 @@ When the `match` expression is done, its scope ends, and so does the scope of
 the inner `y`. The last `println!` produces `at the end: x = Some(5), y = 10`.
 
 To create a `match` expression that compares the values of the outer `x` and
-`y`, rather than introducing a shadowed variable, we would need to use a match
-guard conditional instead. We’ll talk about match guards later in the [“Extra
-Conditionals with Match Guards”](#extra-conditionals-with-match-guards)<!--
-ignore --> section.
+`y`, rather than introducing a new variable which shadows the existing `y`
+variable, we would need to use a match guard conditional instead. We’ll talk
+about match guards later in the [“Extra Conditionals with Match
+Guards”](#extra-conditionals-with-match-guards)<!-- ignore --> section.
 
 ### Multiple Patterns
 
@@ -503,8 +503,8 @@ pattern as `Some(y)`, which would have shadowed the outer `y`, we specify
 `Some(n)`. This creates a new variable `n` that doesn’t shadow anything because
 there is no `n` variable outside the `match`.
 
-The match guard `if n == y` is not a pattern and therefore doesn’t introduce
-new variables. This `y` *is* the outer `y` rather than a new shadowed `y`, and
+The match guard `if n == y` is not a pattern and therefore doesn’t introduce new
+variables. This `y` *is* the outer `y` rather than a new `y` shadowing it, and
 we can look for a value that has the same value as the outer `y` by comparing
 `n` to `y`.