src/doc/reference/src/expressions/grouped-expr.md

   1 # Grouped expressions
   2
   3 > **<sup>Syntax</sup>**\
   4 > _GroupedExpression_ :\
   5 > &nbsp;&nbsp; `(` [_InnerAttribute_]<sup>\*</sup> [_Expression_] `)`
   6
   7 An expression enclosed in parentheses evaluates to the result of the enclosed expression.
   8 Parentheses can be used to explicitly specify evaluation order within an expression.
   9
  10 An example of a parenthesized expression:
  11
  12 ```rust
  13 let x: i32 = 2 + 3 * 4;
  14 let y: i32 = (2 + 3) * 4;
  15 assert_eq!(x, 14);
  16 assert_eq!(y, 20);
  17 ```
  18
  19 An example of a necessary use of parentheses is when calling a function pointer that is a member of a struct:
  20
  21 ```rust
  22 # struct A {
  23 #    f: fn() -> &'static str
  24 # }
  25 # impl A {
  26 #    fn f(&self) -> &'static str {
  27 #        "The method f"
  28 #    }
  29 # }
  30 # let a = A{f: || "The field f"};
  31 #
  32 assert_eq!( a.f (), "The method f");
  33 assert_eq!((a.f)(), "The field f");
  34 ```
  35
  36 ## Group expression attributes
  37
  38 [Inner attributes] are allowed directly after the opening parenthesis of a group expression in the same expression contexts as [attributes on block expressions].
  39
  40 [Inner attributes]: ../attributes.md
  41 [_Expression_]: ../expressions.md
  42 [_InnerAttribute_]: ../attributes.md
  43 [attributes on block expressions]: block-expr.md#attributes-on-block-expressions