projects / rustc.git / blame
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1 | # Tuple types |
| 2 | ||
| 3 | > **<sup>Syntax</sup>**\ | |
| 4 | > _TupleType_ :\ | |
| 5 | > `(` `)`\ | |
| 6 | > | `(` ( [_Type_] `,` )<sup>+</sup> [_Type_]<sup>?</sup> `)` | |
| 7 | ||
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8 | The *tuple type* is a structural type[^1] for heterogeneous lists of other |
| 9 | types. Each entry in the list is an *element*[^2] of the tuple. The position of | |
| 10 | the element makes it the *nth element* using zero (`0`) as the initial index. | |
| 13cf67c4 | 11 | |
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12 | The number of elements determines the arity of the tuple. A tuple with `n` |
| 13 | elements is called an `n-ary tuple`. For example, a tuple with 2 elements is a | |
| 14 | 2-ary tuple. | |
| 13cf67c4 | 15 | |
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16 | For convenience and historical reasons, the tuple type with no elements (`()`) |
| 17 | is often called *unit* or *the unit type*. It's one value is also called *unit* | |
| 18 | or *the unit value*. | |
| 13cf67c4 | 19 | |
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20 | Tuple types are written by listing the types of their elements in a |
| 21 | parenthesized, comma-separated list. 1-ary tuples require a comma after their | |
| 22 | element type to be disambiguated with a [parenthesized type]. | |
| 13cf67c4 | 23 | |
| 29967ef6 | 24 | Some examples of tuple types: |
| 13cf67c4 | 25 | |
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26 | * `()` (unit) |
| 27 | * `(f64, f64)` | |
| 28 | * `(String, i32)` | |
| 29 | * `(i32, String)` (different type from the previous example) | |
| 30 | * `(i32, f64, Vec<String>, Option<bool>)` | |
| 13cf67c4 | 31 | |
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32 | Values of this type are constructed using a [tuple expression]. Furthermore, |
| 33 | various expressions will produce the unit value if there is no other meaningful | |
| 34 | value for it to evaluate to. Tuple elements can be accessed by either a [tuple | |
| 35 | index expression] or [pattern matching]. | |
| 36 | ||
| 37 | [^1]: Structural types are always equivalent if their internal types are | |
| 38 | equivalent. For a nominal version of tuples, see [tuple structs]. | |
| 39 | [^2]: Element is equivalent to field, except numerical indexes instead of | |
| 40 | identifiers | |
| 13cf67c4 | 41 | |
| 416331ca | 42 | [_Type_]: ../types.md#type-expressions |
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43 | [parenthesized type]: ../types.md#parenthesized-types |
| 44 | [pattern matching]: ../patterns.md#tuple-patterns | |
| 45 | [tuple expression]: ../expressions/tuple-expr.md#tuple-expressions | |
| 46 | [tuple index expression]: ../expressions/tuple-expr.md#tuple-indexing-expressions | |
| 47 | [tuple structs]: ./struct.md |