For now, this reference is a best-effort document. We strive for validity and completeness, but are not yet there. In the future, the docs and lang teams will work together to figure out how best to do this. Until then, this is a best-effort attempt. If you find something wrong or missing, file an issue or send in a pull request.

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_variables)]
#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_variables)]
#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_variables)]
#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);
#}