Put the same type constraints on multiple types at once

user_8933345 0
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I have a lot of type constraints, and I would like to make it more readable. For example, is there a way to simplify this:

<P: Serialize + Clone + Eq + std::hash::Hash + std::fmt::Display, E: Serialize + Clone + Eq + std::hash::Hash + std::fmt::Display>

Can I remove this duplication somehow, maybe with a where statement to make it something like this:

where P + E: Serialize + Clone + Eq + std::hash::Hash + std::fmt::Display

It just seems wrong to have it so large.

rust generics
1 Answers

There's not currently any way to combine type constraints like you're hoping for. However, you can at least consolidate the boilerplate a little bit by defining your own trait and a blanket implementation, like this:

trait Data: Serialize + Clone + Eq + std::hash::Hash + std::fmt::Display {}
impl<T> Data for T where T: Serialize + Clone + Eq + std::hash::Hash + std::fmt::Display {}

This will then allow you to write type constraints like this:

where P: Data, E: Data

Note that the original type constraints must still be replicated on both the trait definition and the implementation, to ensure that 1. types implementing the trait also expose the necessary behavior, and 2. the implementation only applies to types that implement the necessary traits.

Here's an example in the playground.

user_40725090
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