What is the proper use of boost::fusion::push_back?
- by Kyle
// ... snipped includes for iostream and fusion ...
namespace fusion = boost::fusion;
class Base
{
protected: int x;
public: Base() : x(0) {}
void chug() {
x++;
cout << "I'm a base.. x is now " << x << endl;
}
};
class Alpha : public Base
{
public:
void chug() {
x += 2;
cout << "Hi, I'm an alpha, x is now " << x << endl;
}
};
class Bravo : public Base
{
public:
void chug() {
x += 3;
cout << "Hello, I'm a bravo; x is now " << x << endl;
}
};
struct chug {
template<typename T>
void operator()(T& t) const
{
t->chug();
}
};
int main()
{
typedef fusion::vector<Base*, Alpha*, Bravo*, Base*> Stuff;
Stuff stuff(new Base, new Alpha, new Bravo, new Base);
fusion::for_each(stuff, chug()); // Mutates each element in stuff as expected
/* Output:
I'm a base.. x is now 1
Hi, I'm an alpha, x is now 2
Hello, I'm a bravo; x is now 3
I'm a base.. x is now 1
*/
cout << endl;
// If I don't put 'const' in front of Stuff...
typedef fusion::result_of::push_back<const Stuff, Alpha*>::type NewStuff;
// ... then this complains because it wants stuff to be const:
NewStuff newStuff = fusion::push_back(stuff, new Alpha);
// ... But since stuff is now const, I can no longer mutate its elements :(
fusion::for_each(newStuff, chug());
return 0;
};
How do I get for_each(newStuff, chug()) to work?
(Note: I'm only assuming from the overly brief documentation on boost::fusion that I am supposed to create a new vector every time I call push_back.)
