Why not make it private or protected? You'll find an answer inside function foo. In other words, base class calls a function defined in a derived class directly. Now, let's find an easiest way for a user to hide implementation details of Derived. It should be very easy; otherwise, users won't use it. It can be a bit trickier for the author of Base but it still should be easy to follow. The most obvious way of achieving this is to establish a friendship between Base and Derived :. This solution is not perfect for one simple reason: the friend declaration is proportional to the number of template parameters of Base class template.
It might get quite long if you add more parameters. To get rid of this problem one can fix the length of the friend declaration by introducing a non-template Accessor that forwards calls:.
A first step of this call chain is always successful because the Base is a friend of Accessor :. We are interested only in a second alternative:. This approach is taken by several boost libraries. Even though this solution is simple, there is a way to omit the friend declaration.
This effectively emulates the virtual function call system at compile time without the costs in size or function call overhead VTBL structures, and method lookups, multiple-inheritance VTBL machinery at the disadvantage of not being able to make this choice at runtime.
Method chaining, also known as named parameter idiom, is a common syntax for invoking multiple method calls in object-oriented programming languages. Fluent interface Method cascading Smalltalk Syntax programming languages Object-oriented programming. Expense Repeating decimal Curiously recurring template pattern Recursion Recurring dream. As mentioned earlier, the main advantage of this technique is that the base class have access to the derived class methods.
Why is that? Although these functionalities can be implemented as non-member function or non-member template functions, those are hard to know about when you check the interface of a class.
Then even though you have one pair of static counters tracking the created and alive objects, you can have separate counters for separate types. All this, because the Counter is a template base class, that you specialize with the derived class as such:. You can avoid virtuals, so you can avoid the runt0time cost of virtual tables in your code by using static interfaces and, surprise, surprise, the CRTP pattern.
We want to model vehicles and in the example, the interface will have one method, getNumberOfWheels :. If you really want to spare runtime, this technique might help you a bit.
The base class knows nothing about the derived course, which might not also have been written when the base class code was written and assembled. We aim to collect all the knowledge the World Wide Web has to offer. Terms and Condition. Privacy Policy.
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