refuel | A simple update framework for Java | Runtime Evironment library

Can a C++ interface inherit from a class with full implementation?

The C++ language doesn't distinguish between interfaces and other classes. The distinction is purely conventional. Thus from one perspective it would be correct to say that C++ interface cannot [whatever] because there is no such thing as C++ interface.

If we consider an interface as an abstract concept, then the answer depends on how one chooses to interpret the concept, and to precisely specify it in terms of the language. If the interpretation is that an interface class has only pure virtual member functions (and this is a common interpretation), then CarInterface is not an interface because it has non-pure-virtual member functions through inheritance.

In the c++ guidelines

I suppose that you intend to refer to the "C++ Core Guidelines". This is how the concepts are defined there:

Note Definition:

• interface inheritance is the use of inheritance to separate users from implementations, in particular to allow derived classes to be added and changed without affecting the users of base classes.
• implementation inheritance is the use of inheritance to simplify implementation of new facilities by making useful operations available for implementers of related new operations (sometimes called “programming by difference”).

A pure interface class is simply a set of pure virtual functions; see I.25.

This is a little bit vague, but I would interpret that CarInterface is a form of both interface inheritance, and implementation inheritance, and it is not a pure interface.

Below the definitions, as well as in section I.25, the guidelines demonstrate such mixed inheritance as a bad example, and suggests an alternative that uses a pure interface instead.

Your example could achieve both pure interfaces, and reuse (which is what your Vehicle class presumably is for) by using virtual inheritance:

I'm updating the answer based on the comments

First thing, I would make sure my JSON properties are consistent across objects:

If you don't want to change things up too much, one easy way would be to simply accumulate the user input with another variable, and pass that value into the function method instead of the user input that updates on each loop. So for example, outside of the do-while loop you would have:

Here is my try, you can change the initial value from 0 to what you want.

As you could guess it's to do with your constraints. This is how your views look currently. UIstackViews are self-sizing to their content. UIViews need to be given height and width information.

This is after I made adjustments.

getAll() is returning a LiveData. The actual database query is being done on a background thread. That will take some time to complete. In the meantime, value is null. You, however, are assuming that it will complete immediately. So, you try using value immediately, and you crash with a NullPointerException.

Please observe() the LiveData.

when you have 2 observables, you can use switchMap operator

The result of a query is always a document (map index). So the original query should actually be:

A return statement must be the last statement in a block.

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