Question

I have a configuration class that I want to pass to another class (called Use) in a constructor. I want to store the configuration class inside of the Use class as a private member variable. I would like it to be const.

So far, I have this code:

class Configuration{
private:
    int value1_;
public:
    Configuration();
    Configuration(int value1){value1_=value1;}
    int value1() const {
        return value1_;
    }
};

class Use{
private:
    //const me
    Configuration config_;
    int something_;
public:
    Use(Configuration &config){
        config_=config;
    }

    void doSomething(){
        something_+=config_.value1();
    }
};

I want to const Use::config_, but every way that I try ends in confusing compile errors. How do I do it?

Answer 1

The best way to support this is to use a reference

class Use{
private:
    const Configuration& config_;
    int something_;
public:
    Use(const Configuration &config) : 
      config_(config), 
      something_(0) {

    }

    void doSomething(){
        something_+=config_.value1();
    }
};

One item that needs to be a bit clearer in the question is the relationship between Configuration and Use instances. If there is one Configuration which is meant to be shared amongst all Use instances then a reference (as I outlined) is the most appropriate choice. In that scenario though you need to ensure that Configuration outlives all Use instances that take a reference to it.

On the other hand if Configuration is meant to be one per Use instance then a non-reference solution is probably more appropriate