The trait cannot be made into an object

I have the following code:

extern crate futures; // 0.1.24

use futures::Future;
use std::io;

struct Context;

pub trait MyTrait {
    fn receive(context: Context) -> Future;
}

pub struct MyStruct {
    my_trait: MyTrait,
}

When I try to compile it I get the error message:

error[E0038]: the trait MyTrait cannot be made into an object
--> src/lib.rs:13:5
|
13 | my_trait: MyTrait,
| ^^^^^^^^^^^^^^^^^ the trait MyTrait cannot be made into an object
|
= note: method receive has no receiver


I think I know why it happens, but how do I refer to the trait from the struct? Is it possible? Maybe there are other ways to implement the same behavior?

You can either add a type parameter to your struct, as in Zernike's answer, or use a trait object.

Using the type parameter is better for performance because each value of T will create a specialized copy of the struct, which allows for static dispatch. A trait object uses dynamic dispatch so it lets you swap the concrete type at runtime.

The trait object approach looks like this:

pub struct MyStruct {
    my_trait: &'a dyn MyTrait,
}

Or this:

pub struct MyStruct {
    my_trait: Box,
}

However, in your case, MyStruct cannot be made into an object because receive is a static method. You'd need to change it to take &self or &mut self as its first argument for this to work. There are also other restrictions.

Stack Overflow Q#45116984, score: 46