Syntax
GroupedExpression :
(Expression)
A parenthesized expression wraps a single expression, evaluating to that expression.
The syntax for a parenthesized expression is a (, then an expression, called the enclosed operand, and then a ).
Parenthesized expressions evaluate to the value of the enclosed operand. Unlike other expressions, parenthesized expressions are both place expressions and value expressions. When the enclosed operand is a place expression, it is a place expression and when the enclosed operand is a value expression, it is a value expression.
Parentheses can be used to explicitly modify the precedence order of subexpressions within an expression.
An example of a parenthesized expression:
let x: i32 = 2 + 3 * 4; // not parenthesized
let y: i32 = (2 + 3) * 4; // parenthesized
assert_eq!(x, 14);
assert_eq!(y, 20);An example of a necessary use of parentheses is when calling a function pointer that is a member of a struct:
# struct A {
# f: fn() -> &'static str
# }
# impl A {
# fn f(&self) -> &'static str {
# "The method f"
# }
# }
# let a = A{f: || "The field f"};
#
assert_eq!( a.f (), "The method f");
assert_eq!((a.f)(), "The field f");