c++ code refactoring using function objects

Question

I have some functionality that returns a value based on values that are set once at start up (in constructor). As these conditional value are only set once, I dont want to be checking them all the time. Is there a way to do the if-check only once and then dont do it again and again using function objects or some other mechanism?

class MyValue {
    bool myVal; //set only once in the constructor
    int myval1; //often updates
    int myval2; //often updates


    myValue(bool val, int val1, int val2)
    {
        myVal = val; // only place where myVal is set

        // this value changes often in other functions not shown here
        myval1 = val1;

        // this value changes often in other functions not shown here
        myval2 = val2;
    }

    int GetMyValue() //often called
    {
        if(myval)    /* Is there a way I dont have to do an if check here? 
                        and simply write a return statement? */
            return myval1;

        return myval2;
    }    
};

can you perhaps use just a single value int myval and set it using myval = val ? val1 : val2; in the constructor? — villintehaspam
– villintehaspam, Commented Jan 27, 2016 at 19:55
"set once at start-up" Are they known at compile-time? Related: Can you use C++11? — AndyG
– AndyG, Commented Jan 27, 2016 at 19:56
Don't engage in premature optimizations. Branch prediction makes wonders. That being said, you can have a pointer to one or another, set it at construction time and than derefrence for return. — SergeyA
– SergeyA, Commented Jan 27, 2016 at 19:56
yes I can use c++11. the value is not known at compile time as it is based on userinput. both myval1 and myval2 need to be stored separately as they have other uses. — bsobaid
– bsobaid, Commented Jan 27, 2016 at 19:57
Ok, that info was originally missing. You can set a pointer to the int you are interested in depending on the bool param and have GetMyValue return *ptrToCorrectMyVal — villintehaspam
– villintehaspam, Commented Jan 27, 2016 at 20:00

MiMo · Accepted Answer · 2016-01-27 20:15:20Z

1

Use a pointer:

class MyValue
{
   int* myVal;
   int myval1; //often updates
   int myval2; //often updates

  myValue(bool val, int val1, int val2)
  {
     if (val) { 
         myVal = &myval1; 
     } else { 
         myVal = &myval2 
     }
     myval1 = val1;
     myval2 = val2;
  }

  int GetMyValue() //often called
  {
     return *myval;
  }

};

(or even better a reference as in Rabbid76 answer)

edited Jan 27, 2016 at 20:15

answered Jan 27, 2016 at 20:03

MiMo

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4 Comments

bsobaid Over a year ago

I will prefer not to introduce a new global variable. can function objects help in this situation?

MiMo Over a year ago

I think you would still need a variable to store the function object instance

bsobaid Over a year ago

i am ok with storing function object instance.

AndyG Over a year ago

@bsobaid: How is storing a function object instance any better than storing an int*?

Rabbid76 · Accepted Answer · 2016-01-27 20:11:42Z

1

Use a member which is either a reference to myval1 or to myval2, the referenc has to be initialized once in the constructor:

class MyValue
{
    bool myVal; //set only once in the constructor
    int myval1; //often updates
    int myval2; //often updates
    int &valref;

public:
    MyValue( bool val, int val1, int val2 )
        : myVal( val )
        , myval1( val1 )
        , myval2( val2 )
        , valref( val ? myval1 : myval2 )
    {}

    int GetMyVal() { return valref; }
};

edited Jan 27, 2016 at 20:11

answered Jan 27, 2016 at 20:06

Rabbid76

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