What design pattern is this?

Question

Several years ago, I used to create interfaces like this :

class Base
{
  public:
    virtual ~Base
    {
    }

    void foo()
    {
      doFoo();
    }

  private:
    virtual void doFoo() = 0;
};

then a derived would be :

class Derived : public Base
{
  public:
    virtual ~Derived()
    {
    }

  private:
    virtual void doFoo()
    {
    }
};

I am sure I saw this as a design pattern somewhere, but now I can not find it anywhere, and can not remember how it is called.

So, how is this design pattern called?

Answer 1

Your foo method shouldn't be virtual. And in this case the design pattern is called NVI - non-virtual interface

Answer 2

This is the template method pattern. Relevant excerpt from Wikipedia:

A template method defines the program skeleton of an algorithm. One or more of the algorithm steps can be overridden by subclasses to allow differing behaviors while ensuring that the overarching algorithm is still followed.

I've seen this pattern used a lot to "enforce" calling the base class implementation (which normally has to be done explicitly in the deriving class).