src/doc/reference/src/expressions/tuple-expr.md

   1 # Tuple and tuple indexing expressions
   2
   3 ## Tuple expressions
   4
   5 > **<sup>Syntax</sup>**\
   6 > _TupleExpression_ :\
   7 > &nbsp;&nbsp; `(` [_InnerAttribute_]<sup>\*</sup> _TupleElements_<sup>?</sup> `)`
   8 >
   9 > _TupleElements_ :\
  10 > &nbsp;&nbsp; ( [_Expression_] `,` )<sup>+</sup> [_Expression_]<sup>?</sup>
  11
  12 Tuples are written by enclosing zero or more comma-separated expressions in
  13 parentheses. They are used to create [tuple-typed](types/tuple.html)
  14 values.
  15
  16 ```rust
  17 (0.0, 4.5);
  18 ("a", 4usize, true);
  19 ();
  20 ```
  21
  22 You can disambiguate a single-element tuple from a value in parentheses with a
  23 comma:
  24
  25 ```rust
  26 (0,); // single-element tuple
  27 (0); // zero in parentheses
  28 ```
  29
  30 ### Tuple expression attributes
  31
  32 [Inner attributes] are allowed directly after the opening parenthesis of a
  33 tuple expression in the same expression contexts as [attributes on block
  34 expressions].
  35
  36 ## Tuple indexing expressions
  37
  38 > **<sup>Syntax</sup>**\
  39 > _TupleIndexingExpression_ :\
  40 > &nbsp;&nbsp; [_Expression_] `.` [TUPLE_INDEX]
  41
  42 [Tuples](types/tuple.html) and [struct tuples](items/structs.html) can be
  43 indexed using the number corresponding to the position of the field. The index
  44 must be written as a [decimal literal](tokens.html#integer-literals) with no
  45 underscores or suffix. Tuple indexing expressions also differ from field
  46 expressions in that they can unambiguously be called as a function. In all
  47 other aspects they have the same behavior.
  48
  49 ```rust
  50 # struct Point(f32, f32);
  51 let pair = (1, 2);
  52 assert_eq!(pair.1, 2);
  53 let unit_x = Point(1.0, 0.0);
  54 assert_eq!(unit_x.0, 1.0);
  55 ```
  56
  57 [Inner attributes]: attributes.html
  58 [TUPLE_INDEX]: tokens.html#integer-literals
  59 [_Expression_]: expressions.html
  60 [_InnerAttribute_]: attributes.html
  61 [attributes on block expressions]: expressions/block-expr.html#attributes-on-block-expressions