[pornel]

In Rust objects can dynamically go in and out of having virtual dispatch. The vtable is only in the pointer to the object, so you can add or remove it. Take a non-virtual object, lend it temporarily as a dynamically dispatched object, and then go back to using it directly as a concrete type, without reallocating anything.

That's pretty powerful:

• any type can be used in dynamic contexts, e.g. implement Debug print for an int or a Point, without paying cost of a vtable for each instance.

• you don't rely on, and don't fight, devirtualization. You can decide to selectively use dynamic dispatch in some places to reduce code size, without committing to it everywhere.

• you can write your own trait with your own virtual methods for a foreign type, and the type doesn't have to opt-in to this.