CODEWITHSUNDEEP
c++interfaceabstract-class
Pavel Oganesyan
Pavel Oganesyan

Reputation: 6924

Abstract class as argument (interface case)

I have an abstract class supposed to be an interface, like this:

  class IDataSource
    {
    public:
        virtual double getMeThatDouble() = 0;
    }

and some implementations like

 class IDataSourceStreamer
    {
    public:
        double getMeThatDouble()
          {
            //implementation
          }
    }

The point is that I want to use it as initial parameter in constructor of other classes like

class DataNeeder
{
  public:
       explicit DataNeeder(IDataSource);
}

and here comes the trouble - "parameter of abstract class type is not allowed".

I understand that it's forbidden for particular reason - using abstract class by itself is impossible. So what should I do? Is a method like 

IDataSource.FeedThat(DataNeeder)

an only option? Kinda ugly.

Upvotes: 2

Views: 3442

Answers (1)

Evan Teran
Evan Teran

Reputation: 90422

You need to pass the abstract type as either a reference or a pointer. For example:

class DataNeeder {
public:
    explicit DataNeeder(IDataSource &source) : source_(source) {
    }

    void someMethod() {
        double x = source_.getMeThatDouble();
        // ...
    }

private:
    IDataSource &source_;
}

Then you can have DataNeeder's member functions operate on source_. As I mentioned, you can also use a pointer for this task, but I like to only use pointers for "OUT" parameters and things that can conceivable be NULL.

Upvotes: 11

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