CODEWITHSUNDEEP
c++templates
J Andrew McCormick
J Andrew McCormick

Reputation: 314

Getting values out of a struct which is a type for a class

This is what my code looks like. It is a bit simplified. What I'm trying to/wondering if i can do is eliminate the need for the argument in the property class constructor. i.e. call a no arg constructor and still be able to populate the classes item variable with the struct value1 item variable without adding them as part of the constructors body.

#include <iostream>

using namespace std;

struct value1
{
    const int item;
    value1( int n ) : item(n) { }
};

struct value2 : public value1
{
    value2() : value1(55) { };
};

template <class T>
class property
{
public:
    property(T stuff);
    void print();
private:
    int item;
};

template <class T>
property<T>::property(T stuff) : item(stuff.item) { }

template <class T>
void property<T>::print()
{
    cout << item << endl;
}

int main()
{
    property<value2> *y = new property<value2>(value2());

    y->print();

    return 0;
}

Upvotes: 1

Views: 56

Answers (2)

Pavan Chandaka
Pavan Chandaka

Reputation: 12731

You can achieve using function objects. Please find code below:

struct value1
{
    const int item;
    value1( int n ) : item(n) { }
};

struct value2 : public value1
{
    value2() : value1(55) { };
};

template <class T>
class property
{
public:
    property();
    void operator() (T i)
    {
        item = i.item;
    }
    void print();
private:
    int item;
};

template <class T>
property<T>::property()  { }

template <class T>
void property<T>::print()
{
    cout << item << endl;
}

int main()
{
    property<value2> *y = new property<value2>();
    (*y)(value2());
    y->print();
   return 0;
}

Upvotes: 0

skypjack
skypjack

Reputation: 50540

call a no arg constructor and still be able to populate the classes item variable with the struct value1 item variable without adding them as part of the constructors body

It sounds like you simply want a factory method:

template <class T>
class property {
public:
    property();
    void print();

    static property<T> create(T stuff) {
        property<T> p;
        p.item = stuff.item;
        return p;
    }

private:
    int item;
};

You can invoke it as it follows:

auto p = property<value2>::create(value2());

Even if I'm not sure I got exactly what your requirements are.
Let me know and I'll delete the answer if I didn't understand the question.

Upvotes: 1

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