How can I create a generic type that includes a trait

Question

I find I am using this pattern a lot.

Arc<Mutex<dyn SomeTrait + Send>>;

and so I thought I would do this:

pub type NicePtr<T> = Arc<Mutex<dyn T + Send>>;

but this does not compile

   Compiling rsim v0.1.0 (C:\work\pdp\rsim)
error[E0404]: expected trait, found type parameter `T`
 --> src\common.rs:9:37
  |
9 | pub type NicePtr<T> = Arc<Mutex<dyn T + Send>>;
  |                                     ^ not a trait

I assume this is possible, but I just dont know the correct syntax.

Answer 1

An interesting note is that (it is the thing that you want)

use std::sync::{Arc, Mutex};
pub type NicePtr<T: Send> = Arc<Mutex<T>>;

does compile, but with a warning:

warning: bounds on generic parameters are not enforced in type aliases
 --> src/lib.rs:2:21
  |
2 | pub type NicePtr<T: Send> = Arc<Mutex<T>>;
  |                     ^^^^
  |
  = note: `#[warn(type_alias_bounds)]` on by default
help: the bound will not be checked when the type alias is used, and should be removed
  |
2 - pub type NicePtr<T: Send> = Arc<Mutex<T>>;
2 + pub type NicePtr<T> = Arc<Mutex<T>>;
  |