How do you create a Box when T is a trait-object?

Question

I have the following code

extern crate rand;
use rand::Rng;

pub struct Randomizer {
    rand: Box,
}

impl Randomizer {
    fn new() -> Self {         


        

Answer 1

I also want to post the answer, that one way to deal with this situation is

fn with_rng(rng: &TRand) -> Self {
    let r = Box::new(*rng);
    Randomizer { rand: r }
}

Rust's monomorphism will create the necessary implementation of with_rng replacing TRand by a concrete sized type. In addition, you may add a trait bound requiring TRand to be Sized.