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Range expressions grammar #142

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Oct 16, 2017
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Range expressions grammar #142

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45 changes: 44 additions & 1 deletion src/expressions/range-expr.md
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Original file line number Diff line number Diff line change
@@ -1,7 +1,35 @@
# Range expressions

> **<sup>Syntax</sup>**
> _RangeExpression_ :
> &nbsp;&nbsp; &nbsp;&nbsp; _RangeExpr_
> &nbsp;&nbsp; | _RangeFromExpr_
> &nbsp;&nbsp; | _RangeToExpr_
> &nbsp;&nbsp; | _RangeFullExpr_
>
> _RangeExpr_ :
> &nbsp;&nbsp; [_Expression_] `..` [_Expression_]
>
> _RangeFromExpr_ :
> &nbsp;&nbsp; [_Expression_] `..`
>
> _RangeToExpr_ :
> &nbsp;&nbsp; `..` [_Expression_]
>
> _RangeFullExpr_ :
> &nbsp;&nbsp; `..`

The `..` operator will construct an object of one of the `std::ops::Range` (or
`core::ops::Range`) variants.
`core::ops::Range`) variants, according to the following table:

| Production | Syntax | Type | Range |
|------------------------|---------------|------------------------------|-----------------------|
| _RangeExpr_ | start`..`end | [std::ops::Range] | start &le; x &lt; end |
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Might be worth using <pre> tags to preserve the formatting in the Range column?

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Do you mean to keep the ≤, x and < aligned (like they are in the source code)?

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Yes.

| _RangeFromExpr_ | start`..` | [std::ops::RangeFrom] | start &le; x |
| _RangeToExpr_ | `..`end | [std::ops::RangeTo] | x &lt; end |
| _RangeFullExpr_ | `..` | [std::ops::RangeFull] | - |

Examples:

```rust
1..2; // std::ops::Range
Expand All @@ -18,3 +46,18 @@ let y = 0..10;

assert_eq!(x, y);
```

Ranges can be used in `for` loops:

```rust
for i in 1..11 {
println!("{}", i);
}
```

[_Expression_]: expressions.html

[std::ops::Range]: https://doc.rust-lang.org/std/ops/struct.Range.html
[std::ops::RangeFrom]: https://doc.rust-lang.org/std/ops/struct.RangeFrom.html
[std::ops::RangeTo]: https://doc.rust-lang.org/std/ops/struct.RangeTo.html
[std::ops::RangeFull]: https://doc.rust-lang.org/std/ops/struct.RangeFull.html