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manual: describe structs, split out handling of recursion from enums, deprecate records.

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Graydon Hoare 2012-10-11 11:47:27 -07:00
parent 0673b49b05
commit 9cba4af243
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doc/rust.md
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@ -705,6 +705,7 @@ There are several kinds of item:
* [modules](#modules)
* [functions](#functions)
* [type definitions](#type-definitions)
* [structures](#structures)
* [enumerations](#enumerations)
* [constants](#constants)
* [traits](#traits)
@ -1111,49 +1112,35 @@ that are composite records, each containing two unsigned 8-bit integers
accessed through the components `x` and `y`, and laid out in memory with the
`x` component preceding the `y` component.
### Structures
A _structure_ is a nominal [structure type](#structure-types) defined with the keyword `struct`.
An example of a `struct` item and its use:
~~~~
struct Point {x: int, y: int}
let p = Point {x: 10, y: 11};
let px: int = p.x;
~~~~
### Enumerations
An _enumeration item_ simultaneously declares a new nominal
[enumerated type](#enumerated-types) as well as a set of *constructors* that
can be used to create or pattern-match values of the corresponding enumerated
type.
The constructors of an `enum` type may be recursive: that is, each constructor
may take an argument that refers, directly or indirectly, to the enumerated
type the constructor is a member of. Such recursion has restrictions:
* Recursive types can be introduced only through `enum` constructors.
* A recursive `enum` item must have at least one non-recursive constructor (in
order to give the recursion a basis case).
* The recursive argument of recursive `enum` constructors must be [*box*
values](#box-types) (in order to bound the in-memory size of the
constructor).
* Recursive type definitions can cross module boundaries, but not module
*visibility* boundaries or crate boundaries (in order to simplify the
module system).
An _enumeration_ is a simulatneous definition of a nominal [enumerated type](#enumerated-types) as well as a set of *constructors*,
that can be used to create or pattern-match values of the corresponding enumerated type.
Enumerations are declared with the keyword `enum`.
An example of an `enum` item and its use:
~~~~
enum animal {
dog,
cat
enum Animal {
Dog,
Cat
}
let mut a: animal = dog;
a = cat;
~~~~
An example of a *recursive* `enum` item and its use:
~~~~
enum list<T> {
nil,
cons(T, @list<T>)
}
let a: list<int> = cons(7, @cons(13, @nil));
let mut a: Animal = Dog;
a = Cat;
~~~~
### Constants
@ -2374,22 +2361,6 @@ A value of type `~str` is a Unicode string, represented as a vector of 8-bit
unsigned bytes holding a sequence of UTF-8 codepoints.
### Record types
The record type-constructor forms a new heterogeneous product of values.^[The
record type-constructor is analogous to the `struct` type-constructor in the
Algol/C family, the *record* types of the ML family, or the *structure* types
of the Lisp family.] Fields of a record type are accessed by name and are
arranged in memory in the order specified by the record type.
An example of a record type and its use:
~~~~
type point = {x: int, y: int};
let p: point = {x: 10, y: 11};
let px: int = p.x;
~~~~
### Tuple types
The tuple type-constructor forms a new heterogeneous product of values similar
@ -2414,6 +2385,7 @@ let (a, b) = p;
assert b != ~"world";
~~~~
### Vector types
The vector type-constructor represents a homogeneous array of values of a
@ -2448,16 +2420,88 @@ All accessible elements of a vector are always initialized, and access to a
vector is always bounds-checked.
### Structure types
A `struct` *type* is a heterogeneous product of other types, called the *fields* of the type.
^[`struct` types are analogous `struct` types in C,
the *record* types of the ML family,
or the *structure* types of the Lisp family.]
New instances of a `struct` can be constructed with a [struct expression](#struct-expressions).
The memory order of fields in a `struct` is given by the item defining it.
Fields may be given in any order in a corresponding struct *expression*;
the resulting `struct` value will always be laid out in memory in the order specified by the corresponding *item*.
The fields of a `struct` may be qualified by [visibility modifiers](#visibility-modifiers),
to restrict access to implementation-private data in a structure.
### Enumerated types
An *enumerated type* is a nominal, heterogeneous disjoint union type.^[The
`enum` type is analogous to a `data` constructor declaration in ML or a *pick
ADT* in Limbo.] An [`enum` *item*](#enumerations) consists of a number of
*constructors*, each of which is independently named and takes an optional
tuple of arguments.
An *enumerated type* is a nominal, heterogeneous disjoint union type,
denoted by the name of an [`enum` item](#enumerations).
^[The `enum` type is analogous to a `data` constructor declaration in ML,
or a *pick ADT* in Limbo.]
An [`enum` item](#enumerations) declares both the type and a number of *variant constructors*,
each of which is independently named and takes an optional tuple of arguments.
New instances of an `enum` can be constructed by calling one of the variant constructors,
in a [call expression](#call-expressions).
Any `enum` value consumes as much memory as the largest variant constructor for its corresponding `enum` type.
Enum types cannot be denoted *structurally* as types,
but must be denoted by named reference to an [`enum` item](#enumerations).
### Recursive types
Nominal types -- [enumerations](#enumerated-types) and [structures](#structure-types) -- may be recursive.
That is, each `enum` constructor or `struct` field may refer, directly or indirectly, to the enclosing `enum` or `struct` type itself.
Such recursion has restrictions:
* Recursive types must include a nominal type in the recursion
(not mere [type definitions](#type-definitions),
or other structural types such as [vectors](#vector-types) or [tuples](#tuple-types)).
* A recursive `enum` item must have at least one non-recursive constructor
(in order to give the recursion a basis case).
* The size of a recursive type must be finite;
in other words the recursive fields of the type must be [pointer types](#pointer-types).
* Recursive type definitions can cross module boundaries, but not module *visibility* boundaries,
or crate boundaries (in order to simplify the module system and type checker).
An example of a *recursive* type and its use:
~~~~
enum List<T> {
Nil,
Cons(T, @List<T>)
}
let a: List<int> = Cons(7, @Cons(13, @Nil));
~~~~
### Record types
> **Note:** Records are not nominal types, thus do not directly support recursion, visibility control,
> out-of-order field initialization, or coherent trait implementation.
> Records are therefore deprecared and will be removed in future versions of Rust.
> [Structure types](#structure-types) should be used instead.
The record type-constructor forms a new heterogeneous product of values.
Fields of a record type are accessed by name and are arranged in memory in the order specified by the record type.
An example of a record type and its use:
~~~~
type Point = {x: int, y: int};
let p: Point = {x: 10, y: 11};
let px: int = p.x;
~~~~
Enumerated types cannot be denoted *structurally* as types, but must be
denoted by named reference to an [*enumeration* item](#enumerations).
### Pointer types
@ -2507,6 +2551,7 @@ Raw pointers (`*`)
they exist to support interoperability with foreign code,
and writing performance-critical or low-level functions.
### Function types
The function type-constructor `fn` forms new function types. A function type
@ -2553,10 +2598,6 @@ fn main() {
In this example, the trait `printable` occurs as a type in both the type signature of
`print`, and the cast expression in `main`.
### Struct types
Every struct item defines a type.
### Type parameters
Within the body of an item that has type parameter declarations, the names of its type parameters are types: