CODEWITHSUNDEEP
genericsrusttraits
Joel Reymont
Joel Reymont

Reputation: 871

Simplifying a type signature without using associated types

Is there a way to simplify the type signature here 

pub struct OrderBook<T: PriceLevel, U: PriceLadder<T>> {
    levels: U,
    phantom: PhantomData<T>,
}

such that 

type HashBook = OrderBook<LinkedHashLevel, HashmapLadder<LinkedHashLevel>>;

can be written as follows?

type HashBook = OrderBook<LinkedHashLevel, HashmapLadder>;

I'm aware of associated types but want to be able to use a single price ladder with different price level implementations.

Complete compilable code below...

use std::marker::PhantomData;
use std::collections::HashMap;

pub struct OrderBook<T: PriceLevel, U: PriceLadder<T>> {
    levels: U,
    phantom: PhantomData<T>,
}

impl<T: PriceLevel, U: PriceLadder<T>> OrderBook<T, U> {}

type HashBook = OrderBook<LinkedHashLevel, HashmapLadder<LinkedHashLevel>>;

pub trait PriceLevel {
    fn new() -> Self where Self: Sized;
}

pub trait PriceLadder<T: PriceLevel> {
    fn new() -> Self;
}

pub struct LinkedHashLevel {
}

impl PriceLevel for LinkedHashLevel {
    fn new() -> Self {
        LinkedHashLevel {}
    }
}

pub struct HashmapLadder<T: PriceLevel> {
    levels: HashMap<u64, T>,
}

impl<T: PriceLevel> PriceLadder<T> for HashmapLadder<T> {
    fn new() -> Self {
        HashmapLadder { levels: HashMap::new() }
    }
}

fn main() {}

Upvotes: 1

Views: 67

Answers (1)

malbarbo
malbarbo

Reputation: 11177

I think that is not necessary to change the type signature. Considering what you sad:

I'm aware of associated types but want to be able to use a single price ladder with different implementations of price level.

Maybe it is enough to create a type type alias parametrized by the price level implementation and with a fixed price ladder:

type HashBook<Level> = OrderBook<Level, HashmapLadder<Level>>;

Upvotes: 2

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