Tuple and index expressions - The Rust Reference

# Tuple and tuple indexing expressions

## Tuple expressions

> Syntax
> TupleExpression :
> `(` InnerAttribute* TupleElements? `)`

> TupleElements :
> ( Expression `,` )+ Expression?

Tuples are written by enclosing zero or more comma-separated expressions in parentheses. They are used to create tuple-typed values.

    #![allow(unused)]
    fn main() {
    (0.0, 4.5);
    ("a", 4usize, true);
    ();
    }

You can disambiguate a single-element tuple from a value in parentheses with a comma:

    #![allow(unused)]
    fn main() {
    (0,); // single-element tuple
    (0); // zero in parentheses
    }

### Tuple expression attributes

Inner attributes are allowed directly after the opening parenthesis of a tuple expression in the same expression contexts as attributes on block expressions.

## Tuple indexing expressions

> Syntax
> TupleIndexingExpression :
> Expression `.` TUPLE_INDEX

Tuples and struct tuples can be indexed using the number corresponding to the position of the field. The index must be written as a decimal literal with no underscores or suffix. Tuple indexing expressions also differ from field expressions in that they can unambiguously be called as a function. In all other aspects they have the same behavior.

    #![allow(unused)]
    fn main() {
    struct Point(f32, f32);
    let pair = (1, 2);
    assert_eq!(pair.1, 2);
    let unit_x = Point(1.0, 0.0);
    assert_eq!(unit_x.0, 1.0);
    }