the danger comes from code like so: void foo(boost::shared_ptr<entity> p) { ... } void bar() { entity* e = new entity; foo(e); delete e; } Allowing a pointer to be converted to a shared_ptr implicitly could cause serious bugs. You could shorten things with this (untested) function: template <typename T> boost::shared_ptr<T> make_sp(T* p) { return boost::shared_ptr<T>(p); }

-----Original Message----- From: Maurizio Colucci [mailto:seguso@email.it] Sent: Friday, March 28, 2003 8:36 AM To: Boost-Users@yahoogroups.com Subject: [Boost-Users] Why "explicit" in shared_ptr's constructor?

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<shared_ptr<entity> > 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)));

which is less readable and, IMHO, barely tolerable on the long run: too much typing.

It seems that the reason is the explicit keyword in the constructor. My question is: why? what was the danger without the explicit?

Thank you very much for any info,

Maurizio

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