structs.md

Structs

^Syntax
Struct :
      StructStruct
   | TupleStruct

StructStruct :
   struct IDENTIFIER  GenericParams^? WhereClause^? ( { StructFields^? } | ; )

TupleStruct :
   struct IDENTIFIER  GenericParams^? ( TupleFields^? ) WhereClause^? ;

StructFields :
   StructField (, StructField)^* ,^?

StructField :
   OuterAttribute^*
   Visibility^?
   IDENTIFIER : Type

TupleFields :
   TupleField (, TupleField)^* ,^?

TupleField :
   OuterAttribute^*
   Visibility^?
   Type

A struct is a nominal struct type defined with the keyword struct. A struct declaration defines the given name in the type namespace of the module or block where it is located.

An example of a struct item and its use:

struct Point {x: i32, y: i32}
let p = Point {x: 10, y: 11};
let px: i32 = p.x;

A tuple struct is a nominal tuple type, and is also defined with the keyword struct. In addition to defining a type, it also defines a constructor of the same name in the value namespace. The constructor is a function which can be called to create a new instance of the struct. For example:

struct Point(i32, i32);
let p = Point(10, 11);
let px: i32 = match p { Point(x, _) => x };

A unit-like struct is a struct without any fields, defined by leaving off the list of fields entirely. Such a struct implicitly defines a constant of its type with the same name. For example:

struct Cookie;
let c = [Cookie, Cookie {}, Cookie, Cookie {}];

is equivalent to

struct Cookie {}
const Cookie: Cookie = Cookie {};
let c = [Cookie, Cookie {}, Cookie, Cookie {}];

The precise memory layout of a struct is not specified. One can specify a particular layout using the repr attribute.