writes:
Dear all,
On a project of mine, I started to use Boost.Flyweight. I would like
users of my class to only be able to instantiate objects of my class by
using the Boost.Flyweight mechanism. For this, I make my class
constructor private. However, when doing so the corresponding flyweight
factory also cannot instantiate my class. What classes do I need to
`friend` in order to make this work?
You need to do
template
friend struct boost::flyweights::detail::optimized_key_value;
but this is highly unadvisable, as you're relying on undocumented
classes that might change without prior notice in future versions
of the library. An alternative is to simply make the whole class
implementation private:
class X {
struct impl
{
impl(int x):m_data(x){};
int data() const { return m_data; }
int m_data;
};
struct key_extractor
{
int operator()(const impl& x) const { return x.data(); }
};
public:
typedef boost::flyweights::flyweight<
boost::flyweights::key_value<
int,
impl,
key_extractor
>
> flyweight;
};
int main()
{
auto my_x = X::flyweight(42);
return 0;
}
Joaquín M López Muñoz
Telefónica
