Trait objects / dyn T / Arbitrary implementers

The type &dyn MyTrait, where MyTrait is a trait, is supported. It will be translated to MyTrait on Dart side.

This is especially helpful when we want to have an argument that accepts anything that implements the trait.

Example

pub trait MyTrait {}
impl MyTrait for MyStructOne {}
impl MyTrait for MyStructTwo {}

pub fn f(a: &dyn MyTrait) {}

Then, the generated Dart signature is like:

void f(MyTrait a) => ...;

And we can use it like:

MyStructOne one = ...;
MyStructTwo two = ...;

f(one); // allowed
f(two); // also allowed