[Boost-users] [BGL] Default-constructibility of vertices

Subject: [Boost-users] [BGL] Default-constructibility of vertices
From: Kelvin Chung (kelvSYC_at_[hidden])
Date: 2011-12-12 20:42:20

Suppose I have a class hierarchy, like so:

struct Foo {
        virtual Output doSomething(const Input& in);
};

class CompositeFoo {
        std::vector<Foo*> fooList;	// Use your favorite smart pointer standin 
for Foo* here
public:
        Output doSomething(const Input& in);
};

Now, suppose I have a functor:

class Functor {
        Foo* foo;
        Input input;	// assume Input is copyable
public:
        Output operator()() { foo->doSomething(input); }
};

Now, the structure of doSomething() calls leads to a DAG structure with 
Functor as the vertices.  What I want to do is create a graph with BGL 
that shows that structure, before topologically sorting it and doing 
other stuff with it.  However, it would appear that the vertices of the 
graph (which I would assume to be of type 
boost::adjacency_list<boost::vecS, boost::vecS, boost::directedS, 
Functor>) must be default-constructible, which Functor is clearly not.  
Is there a nice workaround to this without changing the vertex type to 
Functor* (again, use your favorite smart pointer standin for Functor* 
here)?