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

On Mon, 12 Dec 2011, Kelvin Chung wrote:

Suppose I have a class hierarchy, like so:

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

class CompositeFoo { std::vector 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) 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)?

Have you tried using the two-parameter version of add_vertex() (with vertex property value as the first parameter)? I don't know if that would work, but it might. The requirements for property types (at least for old-style properties) say that they need to be default constructible, though, so you might need to use a pointer. Is the assumption on Input in your example that it isn't default constructible? Otherwise, Functor should be as well. -- Jeremiah Willcock