storing fixed known data in classes (c++) [closed] - c++

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I have this class to store fixed known data. Each object should have its own unique id in such way that, when the user calls Belt belt(1), an object with the correct values of name, perimeter, nOfPoints is created. Is there any better way to define these other parameters without a switch-case? Should I design this in another way? What are the disadvantages of such implementation?
class Belt {
private:
int _id;
std::string _name;
int _perimeter;
int _nOfPoints;
public:
Belt(int id){
_id = id;
switch (id)
{
case 1:
_name = "NEO";
_perimeter = 100;
_nOfPoints = 10;
break;
case 2:
_name = "PED";
_perimeter = 200;
_nOfPoints = 12;
break;
case 3:
_name = "ADT";
_perimeter = 400;
_nOfPoints = 20;
break;
}
}
};

Answer 1

Is there any better way to define these other parameters without a switch-case?
You could use a private static map to hold your prototypes:
class Belt {
private:
static const std:map<int,Belt> prototypes;
int _id;
std::string _name;
int _perimeter;
int _nOfPoints;
Belt(int id, const std::string name, int perimeter, int nOfPoints)
: _id(id), _name(name), _perimeter(perimeter), _nOfPoints(nOfPoints) {}
public:
Belt(int id) {
_id = id;
_name = prototypes[_id]._name;
_perimeter= prototypes[_id]._perimeter;
_nOfPoints= prototypes[_id]._nOfPoints;
// Or simpler instead of the lines above:
// *this = prototypes[id];
}
};
const std:map<int,Belt> Belt::prototypes = {
{ 1 , Belt(1,"NEO",100,10) }
, { 2 , Belt(2,"PED",200,12) }
, { 3 , Belt(3,"ADT",400,20) }
};
Also you might be interested to have a look at the Prototype Design Pattern. That's an alternative technique you can use, and gives you better flexibility.

Answer 2

If you're only going to have a fixed set of values to deal with, I'd suggest making static const instances in Belt. This has the advantage of avoiding any lookup overhead, and dealing with invalid input (e.g., somebody passes INT_MAX to your constructor). For example:
class Belt {
private:
int _id;
std::string _name;
int _perimeter;
int _nOfPoints;
Belt(int id, name, perimeter, nOfPoints)
: _id{id}, _name{std::move(name)}
, _perimeter{perimeter}, _nOfPoints{nOfPoints} { }
public:
static const Belt neo(1, "NEO", 100, 10);
static const Belt ped(2, "PED", 200, 12);
// ...
};
A user can create a local Belt by copying one of the existing objects, and still perform any local manipulations that they need.
int main() {
auto myBelt = Belt::neo;
myBelt.some_member_function();
}