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#![feature(optin_builtin_traits)] | |
use std::marker::PhantomData; | |
trait Lookup<K> { | |
type V; | |
fn get(&self) -> &Self::V; | |
} | |
struct Nil; | |
struct Cons<K, V, T> { | |
pd: PhantomData<K>, | |
value: V, | |
tail: T | |
} | |
impl<K, V, T> Cons<K, V, T> { | |
fn push<K2, V2>(self, value: V2) -> Cons<K2, V2, Self> { | |
Cons { | |
pd: PhantomData, | |
value: value, | |
tail: self | |
} | |
} | |
} | |
impl Nil { | |
fn push<K, V>(self, value: V) -> Cons<K, V, Self> { | |
Cons { | |
pd: PhantomData, | |
value: value, | |
tail: self | |
} | |
} | |
} | |
trait NotSame {} | |
impl NotSame for .. {} | |
impl<T> !NotSame for (T, T) {} | |
impl<K1, K2, V, T> Lookup<K1> for Cons<K2, V, T> | |
where T: Lookup<K1>, (K1, K2): NotSame | |
{ | |
type V = <T as Lookup<K1>>::V; | |
fn get(&self) -> &Self::V { self.tail.get() } | |
} | |
impl<K, V, T> Lookup<K> for Cons<K, V, T> { | |
type V = V; | |
fn get(&self) -> &V { &self.value } | |
} | |
trait DoLookup { | |
fn lookup<K>(&self) -> &<Self as Lookup<K>>::V where Self: Lookup<K>; | |
} | |
impl<T> DoLookup for T { | |
fn lookup<K>(&self) -> &<Self as Lookup<K>>::V where Self: Lookup<K> { | |
<Self as Lookup<K>>::get(&self) | |
} | |
} | |
fn main() { | |
struct Key1; struct Key2; struct Key3; | |
let table = Nil | |
.push::<Key1, _>(42536) | |
.push::<Key2, _>(false) | |
.push::<Key3, _>("Hello World!"); | |
println!("{:?}", table.lookup::<Key3>()); | |
println!("{:?}", table.lookup::<Key1>()); | |
println!("{:?}", table.lookup::<Key2>()); | |
} |
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