Re: [Boost-Users] Why "explicit" in shared_ptr's constructor?

Maurizio Colucci wrote:

Hello,

I am a newbie user of boost.

I have a question about boost::shared_ptr. Suppose you have a polimorphic list:

class entity{ ...};

class simple_entity : public entity{ public: uint id; simple_entity(uint i) : id(i) {} };

int main(){ list l; ...

I noticed the following code doesn't compile

l.push_back(new simple_entity(1));

too bad, because it was very easy to read, and very similar to the behavior if standard pointers (not to speak about similarity to Java and C#). So I am forced to do

l.push_back(shared_ptr<entity> (new simple_entity(1)));

The idiomatic way to write the above is to use a named variable: shared_ptr<entity> pe(new simple_entity(1)); l.push_back(pe); as explained in http://www.boost.org/libs/smart_ptr/shared_ptr.htm#BestPractices If you want to save typing, consider adding static shared_ptr create(int id) { shared_ptr ps(new simple_entity(id)); return ps; } to simple_entity, allowing you to write l.push_back(simple_entity::create(1)); If entity objects are always supposed to live on the heap, you now have the option to make the simple_entity constructor private or protected, leaving 'create' as the only way to obtain a simple_entity.