All the usual suspects, error handling, sum types, interfaces.
Just a note, I'm yet to see a problem highlighted in the section about interfaces, in particular that changing a concrete type will make it not fit the interface anymore which will result in troubles. It's often used as a tool to make the changes (e.g. change the interface, observe the compilation failure and fix all the occurrences). They way interfaces are usually defined on site as a minimal possible signature - if your code just needs one method, you define a narrow interface and that's it. That also makes it impossible to predict what kind of interface is needed at producer side.
If the argument is that you can fit a wrong struct into the interface, then again, I'm yet to see a real life manifestation of this problem.
Just a note, I'm yet to see a problem highlighted in the section about interfaces, in particular that changing a concrete type will make it not fit the interface anymore which will result in troubles. It's often used as a tool to make the changes (e.g. change the interface, observe the compilation failure and fix all the occurrences). They way interfaces are usually defined on site as a minimal possible signature - if your code just needs one method, you define a narrow interface and that's it. That also makes it impossible to predict what kind of interface is needed at producer side.
If the argument is that you can fit a wrong struct into the interface, then again, I'm yet to see a real life manifestation of this problem.