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Update RFC 195 for RFC 246.

This commit is contained in:
Sean Patrick Santos 2015-02-15 16:03:20 -07:00
parent dfd33cc6e7
commit 3b5abbfd05
1 changed files with 18 additions and 13 deletions
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text/0195-associated-items.md
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@ -9,6 +9,7 @@ more convenient, scalable, and powerful. In particular, traits will consist of a
set of methods, together with:
* Associated functions (already present as "static" functions)
* Associated consts
* Associated statics
* Associated types
* Associated lifetimes
@ -173,7 +174,7 @@ provide a distinct `impl` for every member of this family.
Associated types, lifetimes, and functions can already be expressed in today's
Rust, though it is unwieldy to do so (as argued above).
But associated _statics_ cannot be expressed using today's traits.
But associated _consts_ and _statics_ cannot be expressed using today's traits.
For example, today's Rust includes a variety of numeric traits, including
`Float`, which must currently expose constants as static functions:
@ -191,19 +192,19 @@ trait Float {
```
Because these functions cannot be used in static initializers, the modules for
float types _also_ export a separate set of constants as statics, not using
float types _also_ export a separate set of constants as consts, not using
traits.
Associated constants would allow the statics to live directly on the traits:
Associated constants would allow the consts to live directly on the traits:
```rust
trait Float {
static NAN: Self;
static INFINITY: Self;
static NEG_INFINITY: Self;
static NEG_ZERO: Self;
static PI: Self;
static TWO_PI: Self;
const NAN: Self;
const INFINITY: Self;
const NEG_INFINITY: Self;
const NEG_ZERO: Self;
const PI: Self;
const TWO_PI: Self;
...
}
```
@ -282,13 +283,14 @@ distinction" below.
## Trait bodies: defining associated items
Trait bodies are expanded to include three new kinds of items: statics, types,
and lifetimes:
Trait bodies are expanded to include four new kinds of items: consts, statics,
types, and lifetimes:
```
TRAIT = TRAIT_HEADER '{' TRAIT_ITEM* '}'
TRAIT_ITEM =
... <existing productions>
| 'const' IDENT ':' TYPE [ '=' CONST_EXP ] ';'
| 'static' IDENT ':' TYPE [ '=' CONST_EXP ] ';'
| 'type' IDENT [ ':' BOUNDS ] [ WHERE_CLAUSE ] [ '=' TYPE ] ';'
| 'lifetime' LIFETIME_IDENT ';'
@ -352,7 +354,7 @@ external to the trait.
### Defaults
Notice that associated statics and types both permit defaults, just as trait
Notice that associated consts, statics, and types permit defaults, just as trait
methods and functions can provide defaults.
Defaults are useful both as a code reuse mechanism, and as a way to expand the
@ -430,6 +432,7 @@ lifetime items are allowed:
```
IMPL_ITEM =
... <existing productions>
| 'const' IDENT ':' TYPE '=' CONST_EXP ';'
| 'static' IDENT ':' TYPE '=' CONST_EXP ';'
| 'type' IDENT' '=' 'TYPE' ';'
| 'lifetime' LIFETIME_IDENT '=' LIFETIME_REFERENCE ';'
@ -767,7 +770,8 @@ as UFCS-style functions:
trait Foo {
type AssocType;
lifetime 'assoc_lifetime;
static ASSOC_STATIC: uint;
const ASSOC_CONST: uint;
static ASSOC_STATIC: &'static [uint, ..1024];
fn assoc_fn() -> Self;
// Note: 'assoc_lifetime and AssocType in scope:
@ -776,6 +780,7 @@ trait Foo {
fn default_method(&self) -> uint {
// method in scope UFCS-style, assoc_fn in scope
let _ = method(self, assoc_fn());
ASSOC_CONST // in scope
ASSOC_STATIC // in scope
}
}