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Array and indexing grammar #133

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Dec 1, 2017
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Array and indexing grammar #133

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e09600d
Array and indexing grammar
brauliobz Oct 4, 2017
31471ff
Clarified the multidimensional array access
brauliobz Nov 30, 2017
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23 changes: 22 additions & 1 deletion src/expressions/array-expr.md
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Expand Up @@ -2,6 +2,12 @@

## Array expressions

> **<sup>Syntax</sup>**
> _ArrayExpression_ :
> &nbsp;&nbsp; &nbsp;&nbsp; `[` `]`
> &nbsp;&nbsp; | `[` [_Expression_] ( `,` [_Expression_] )<sup>\*</sup> `,`<sup>?</sup> `]`
> &nbsp;&nbsp; | `[` [_Expression_] `;` [_Expression_] `]`

An _[array](types.html#array-and-slice-types) expression_ can be written by
enclosing zero or more comma-separated expressions of uniform type in square
brackets. This produces and array containing each of these values in the
Expand All @@ -20,11 +26,16 @@ greater than 1 then this requires that the type of `a` is
[1, 2, 3, 4];
["a", "b", "c", "d"];
[0; 128]; // array with 128 zeros
[0u8, 0u8, 0u8, 0u8];
[0u8, 0u8, 0u8, 0u8,];
[[1, 0, 0], [0, 1, 0], [0, 0, 1]]; // 2D array
```

## Array and slice indexing expressions

> **<sup>Syntax</sup>**
> _IndexExpression_ :
> &nbsp;&nbsp; [_Expression_] `[` [_Expression_] `]`

[Array and slice](types.html#array-and-slice-types)-typed expressions can be
indexed by writing a square-bracket-enclosed expression (the index) after them.
When the array is mutable, the resulting
Expand All @@ -43,6 +54,9 @@ _panicked state_ if it fails.
```rust,should_panic
([1, 2, 3, 4])[2]; // Evaluates to 3

let b = [[1, 0, 0], [0, 1, 0], [0, 0, 1]];
b[1][2]; // multidimensional array indexing

let x = (["a", "b"])[10]; // warning: const index-expr is out of bounds

let n = 10;
Expand All @@ -51,3 +65,10 @@ let y = (["a", "b"])[n]; // panics
let arr = ["a", "b"];
arr[10]; // panics
```

The array index expression can be implemented for types other than arrays and slices
by implementing the [Index] and [IndexMut] traits.

[Index]: https://doc.rust-lang.org/std/ops/trait.Index.html
[IndexMut]: https://doc.rust-lang.org/std/ops/trait.IndexMut.html
[_Expression_]: expressions.html