Grouped expressions

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:

#![allow(unused)] fn main() { 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:

#![allow(unused)] fn main() { 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"); }