What are object safe traits in Rust?

Object-safe traits are traits with methods that follow these two rules:

Self is an alias for the type we will be implementing the trait on.

Only object-safe traits can be made into trait objects. To learn more about creating trait objects, check out this answer.

An object-safe trait

pub trait Area {
    /// Returns area as i32 (32-bit
    /// integer)
    fn area(&self) -> i32;
}

Not an object-safe trait

pub trait Clone {
    /// Returns a clone (duplicate)
    /// of the object
    fn clone(&self) -> Self;
}

Example