Sometimes, the Rust compiler cannot determine the size of a trait object at compile time. For example, if a function returns a trait object based on a condition, in such cases, impl Trait is not going to work. This is because the size of the trait object is not known at compile time. In such cases, you can use Box<dyn Trait> to return a trait object.

Box<T> lets you allocate memory on the heap and store the value of T in that memory. Box<dyn Trait> is a trait object that allows you to store a value of any type that implements Trait in the heap.

This is called dynamic dispatch because the method to call is determined at runtime, not at compile time. This is in contrast to static dispatch, where the method to call is determined at compile time.

You need to define a function that returns a Box<dyn Speakable> based on a condition.

Here is what you need to do:

• Define the Speakable trait with a method speak that returns a String.
• Define a struct Dog with two fields: name and breed, both of type String.
• Implement the Speakable trait for Dog to return a string Woof.
• Define a struct Robot with two fields: model and purpose, both of type String.
• Implement the Speakable trait for Robot to return a string Beep boop.
• Finish the function get_speaker that takes a &str parameter and returns either a Dog or a Robot based on the parameter.
• The parameter can either be dog or robot.