The Complete Rust Programming Reference Guide

Trait objects and object safety

Object safety is a set of rules and restrictions that does not allow trait objects to be constructed. Consider the following code:

// object_safety.rstrait Foo {    fn foo();}fn generic(val: &Foo) {}fn main() {}

We get the following error upon compilation:

This brings us to the idea of object safety, which is a set of restrictions that forbids creating a trait object from a trait. In this example, since our type doesn't have a self reference, it's not possible to create a trait object out of it. In this case, to convert any type into a trait object, methods on the type need to be an instance—one that takes self ...