https://github.com/joshuasbrown/selectiveandsafeclasstemplatemethod
The contained code simply displays how to create a container which stores a base class that is able to selectively return the contents of the container in any type.
https://github.com/joshuasbrown/selectiveandsafeclasstemplatemethod
Last synced: 3 months ago
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The contained code simply displays how to create a container which stores a base class that is able to selectively return the contents of the container in any type.
- Host: GitHub
- URL: https://github.com/joshuasbrown/selectiveandsafeclasstemplatemethod
- Owner: JoshuaSBrown
- Created: 2018-10-04T15:28:19.000Z (over 6 years ago)
- Default Branch: master
- Last Pushed: 2018-10-10T21:20:53.000Z (over 6 years ago)
- Last Synced: 2025-01-24T17:26:55.442Z (5 months ago)
- Language: C++
- Size: 9.77 KB
- Stars: 0
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Selective and Safe Class Template Method for Utilizing Polymorphism
The contained code simply displays how to create a polymorphic container which stores a vector of a base class, the container is able to selectively return the contents of the container in any type safely by ensuring that the type is either of base type or is the same type of class that the element was oringinally created as. Or if you want to be even more seletive you can specificaly choose which types you want the the set method to be allowed to store and therefore return.
I will provide an example to explain. Suppose that we have 3 vehicles:
* base - base class vehicle type
* sedan - child of base
* truck - child of base
Now if I have a container class that stores a vector of the base class, I will call it a garage, I can add any of these three vehicle types to the container with no problems by making use of polymorphism.
```
class Vehicle {
public:
Vehicle() {};
};
class Truck : Vehicle {
public:
Truck() {};
};
class Sedan : Vehicle {
public:
Sedan() {};
}
class BaseGarage {
public:
BaseGarage() {};
void parkVehicle(shared_ptr V) {
parked_vehicles.push_back(V);
}
private:
vector> parked_vehicles;
};
```
The problem comes when I try to get the Vehicles out. Let's assume that I create a vehicle of class Truck and park it in the garage. It will be stored as a pointer to the base class. But how do I get it out as a truck when several vehicle types could be stored in the garage. Well I can use a templated method and dynamically cast to the correct type:
```
class Vehicle {
public:
Vehicle() {};
};
class Truck : Vehicle {
public:
Truck() {};
};
class Sedan : Vehicle {
public:
Sedan() {};
}
class BaseGarage {
public:
BaseGarage() {};
void parkVehicle(shared_ptr V) {
parked_vehicles.push_back(V);
}
template
shared_ptr getParkedVehicle(int index){
return dynamic_pointer_cast(parked_vehicles.at(index));
}
private:
vector> parked_vehicles;
};
```
And this is where the problem occurs because say that I put a truck in the garage but I pull it out as a Sedan. Well this code will compile but you end up with a segment fault and no warning. The code in this repo shows how to avoid these segment faults by ensuring that you can only cast to either the base class or the original class of the object. So the truck could be cast to base or truck with no problems but will throw an error if the user tries to cast it to a sedan.
## Compile
To compile the code
```
g++ -o vehicle vehicle.cpp -std=c++11 -Wall -pedantic -Werror
```