元组和索引表达式

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.

(0.0, 4.5);
("a", 4usize, true);
();

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

(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.

# 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);