src/items/structs.md

r[items.struct]
# Structs

r[items.struct.syntax]
```grammar,items
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
```

r[items.struct.intro]
A _struct_ is a nominal [struct type] defined with the keyword `struct`.

r[items.struct.namespace]
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:

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

r[items.struct.tuple]
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:

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

r[items.struct.unit]
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:

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

is equivalent to

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

r[items.struct.layout]
The precise memory layout of a struct is not specified. One can specify a
particular layout using the [`repr` attribute].

[`repr` attribute]: ../type-layout.md#representations
[constant]: constant-items.md
[struct type]: ../types/struct.md
[tuple type]: ../types/tuple.md
[type namespace]: ../names/namespaces.md
[value namespace]: ../names/namespaces.md