struct.md

Struct types

r[type.struct]

r[type.struct.intro] A struct type is a heterogeneous product of other types, called the fields of the type.¹

r[type.struct.constructor] New instances of a struct can be constructed with a struct expression.

r[type.struct.layout] The memory layout of a struct is undefined by default to allow for compiler optimizations like field reordering, but it can be fixed with the repr attribute. In either case, fields may be given in any order in a corresponding struct expression; the resulting struct value will always have the same memory layout.

r[type.struct.field-visibility] The fields of a struct may be qualified by visibility modifiers, to allow access to data in a struct outside a module.

r[type.struct.tuple] A tuple struct type is just like a struct type, except that the fields are anonymous.

r[type.struct.unit] A unit-like struct type is like a struct type, except that it has no fields. The one value constructed by the associated struct expression is the only value that inhabits such a type.

Struct

r[type.struct.value]

r[type.struct.value.intro] A value of a struct type consists of a list of values for each field.

r[type.struct.value.encode-decode] When a value of a struct type is encoded, each field of the struct is encoded at its corresponding offset and each byte that is not within a field of the struct is set to uninit. When a value of a struct type is decoded, each field of the struct is decoded from its corresponding offset. Each byte that is not within a field of the struct is ignored.

Footnotes

1. struct types are analogous to struct types in C, the record types of the ML family, or the struct types of the Lisp family. ↩