Say I have the following classes:
#include <string>
class Item {
public:
Item(std::string name, int id);
virtual int getWeight() = 0;
protected:
std::string name;
const int id;
}
#include <vector>
#include <memory>
#include "Item.h"
class Bucket : Item {
public:
Bucket(std::string name, std::string type, int id) // In the implementation this will call the Constructor of Item
bool operator<(const Bucket& b) const {
return (id < b.id );
}
void addItem(std::shared_ptr<Item> itemm) {
this->weight += item->getWeight();
this->items.push_back(item);
}
int getWeight() override; //this implementation does not matter to the problem
private:
std::string type;
std::vector<std::shared_ptr<Item>> items;
int weight = 0;
}
There are other classes inheriting from class Item aswell, but to make it easier I am only showing the class Bucket.
Now in my main method, I want to iterate over a map, that already contains some entries and call a method that changes one property of the key object.
main.cpp:
#include <map>
#include <memory>
#include <vector>
#include "Item.h"
#include "Bucket.h"
using namespace std;
int main(){
map<Bucket, vector<shared_ptr<Item>>> map; // Imagine this map has some entries
for(auto itr = map.begin(); itr != map.end(); itr++){
for_each(itr->second.begin(), itr->second.begin(), [&itr](shared_ptr<Item> item){
itr->first.addItem(item); // This does not compile, the error will be in the text below
});
}
As told in the code, it does not compile with the following error on line itr->first.addItem(item);:
'this' argument to member function 'addItem' has type 'const Bucket', but function is not marked const.
I can't make the method const, since it is changeing some property of the object and I would get an error there.
I am not sure if I understand this error correctly, but I think the problem is, that as I put a Bucket into a map (Bucket is the key), it becomes const.
If that is the case, is there a way to tell the compiler to use only the id property of Bucket as the const key of the map (Without changeing the map to something like map<int, <pair<Bucket,vector<shared_ptr<Item>>>>>)? Or am I not understanding the main problem here?
