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Clean up E0178 explanation

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GuillaumeGomez committed Jan 6, 2020
1 parent a80e63f commit 99fda5c1cec9ab67c3da197b5679408d2e51d093
Showing with 18 additions and 7 deletions.
  1. +18 −7 src/librustc_error_codes/error_codes/E0178.md
@@ -1,16 +1,27 @@
In types, the `+` type operator has low precedence, so it is often necessary
to use parentheses.
The `+` type operator was used in an ambiguous context.

For example:
Erroneous code example:

```compile_fail,E0178
trait Foo {}
struct Bar<'a> {
w: &'a Foo + Copy, // error, use &'a (Foo + Copy)
x: &'a Foo + 'a, // error, use &'a (Foo + 'a)
y: &'a mut Foo + 'a, // error, use &'a mut (Foo + 'a)
z: fn() -> Foo + 'a, // error, use fn() -> (Foo + 'a)
x: &'a Foo + 'a, // error!
y: &'a mut Foo + 'a, // error!
z: fn() -> Foo + 'a, // error!
}
```

In types, the `+` type operator has low precedence, so it is often necessary
to use parentheses:

```
trait Foo {}
struct Bar<'a> {
x: &'a (Foo + 'a), // ok!
y: &'a mut (Foo + 'a), // ok!
z: fn() -> (Foo + 'a), // ok!
}
```

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