rust - Can I do type introspection with trait objects and then downcast it?

Question

I have a collection of Trait, a function that iterates over it and does something, and then I would like to check the implementor type and if it is of type Foo then downcast it and call some Foo method.

Basically, something similar to Go's type-switch and interface conversion.

Searching around I found about the Any trait but it can only be implemented on 'static types.

To help demonstrate what I want:

let vec: Vec<Box<Trait>> = //

for e in vec.iter() {
    e.trait_method();

    // if typeof e == Foo {
    // let f = e as Foo;
    // f.foo_method();
    //}
}

Answer 1

As you have noticed, downcasting only works with Any trait, and yes, it only supports 'static data. You can find a recent discussion on why it is so here. Basically, implementing reflection for references of arbitrary lifetimes is difficult.

It is also impossible (as of now, at least) to combine Any with your custom trait easily. However, a macro library for automatic implementation of Any for your trait has recently been created. You can also find some discussion on it here.