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Copy constructor - script for MetaTrader 5

DMITRII PECHERITSA

Views:
882
Rating:
votes: 9
Published:
2020.05.24 07:54
Updated:
2020.05.24 11:09

Here is one option that will work in MQL.

The technique is called 'copy constructor'. Make sure that all fields are copied, including complex data types, recursively.

Please refer to the example code below, you will figure out how it works. 

/****************************************************************/
void ClassExample()
  {
   Print(__FUNCTION__);
   A a1;
   A a2=Fa(); //object receive from function
   a1.Work();
   a1.Report(); //1 1 1 1
   a2.Report(); //3 3 3 3
   /*CONTINUE USE OBJECT FROM FUNCTION*/
   a2.Work();
   a2.Report(); //4 4 4 4
   return;
  }
/***************************************************************
   PARTS OF CLASS A*/
struct C {int mx; C():mx(0) {}};
class D {public:int mx; D():mx(0) {} D(D &d):mx(d.mx) {}};
/****************************************************************/
class A
  {
protected:
   int               mx;   //simple
   int               ma[]; //array
   C                 mc;   //struct
   D                 d;    //class
public:
   /*COPY CONSTRUCTOR*/
                     A(A &a):mx(a.mx),d(a.d) {ArrayCopy(ma,a.ma); mc=a.mc;}
   /*EXPLICIT DEFAULT CONSTRUCTOR*/
                     A():mx(0) {}
   /*METHODS*/
   void              Work() {mx++; ArrayResize(ma,mx); mc.mx=mx; d.mx=mx;}
   void              Report() {Print(mx," ",ArraySize(ma)," ",mc.mx," ",d.mx);}
  };
/****************************************************************/
A Fa()
  {
   A a;
   for(int i=0; i<3; i++)
     {a.Work();} //a lot of work
   return a; //class object return
  }
/**/

Want to return a structure?
Structures can be normally updated with function as parameters sent by reference.
If you wish to RETURN a struct with function, it is also possible, but unlike classes, structs do not require an explicit copy constructor.


/****************************************************************/
void StructExample()
  {
   Print(__FUNCTION__);
   B b1;
   B b2=Fb(); //struct receive from function
   b1.mx++;
   /**/
   Print(b1.mx," ",ArraySize(b1.ma)); //  1 0
   Print(b2.mx," ",ArraySize(b2.ma)); // 10 9
   return;
  }
/****************************************************************/
struct B
  {
   int               mx;
   int               ma[];
                     B():mx(0) {} //constructor, not needed formally
  };
/****************************************************************/
B Fb()
  {
   B b;
   for(int i=0; i<10; i++)
     {b.mx++; ArrayResize(b.ma,i);} //work hard
   return b; //struct return
  }
/**/


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