[Boost-users] Indirectly 'recursive' type erasure

Subject: [Boost-users] Indirectly 'recursive' type erasure
From: Samuel Christie (schrist_at_[hidden])
Date: 2014-03-06 19:01:39

I'm trying to create a type erasure concept for a type that has a member
function which can return a custom collection of itself.

Having had little luck with the general formulation, I tried simplifying it
to:

BOOST_TYPE_ERASURE_MEMBER((has_collection), collection, 0);

typedef any<
  mpl::vector<
    copy_constructible<>,
    typeid_<>,
    relaxed,
    has_collection<vector<_self>()>
    >
  > test;

class Test {
public:
  vector<test> collection();
};

However, I get conversion errors if the Test::collection method returns
either vector<Test> or vector<test>; it only seems to match if I have it
literally return vector<_self>, which implies to me that I'm not
understanding what I'm doing, and that _self isn't getting substituted in
this case.

What do I need to do in order to be able to return types that are dependent
on the erasure type? My actual code uses a more indirect relationship, with
the collection method returning a custom erased collection type that has an
erased iterator that can dereference to the equivalent of Test. However,
since there is still a form of cyclic dependency, I'm not really sure what
I can do about it. I've tried using a custom struct based concept that had
direct template arguments in the place of 'boost type erasure member', but
I think I understand that technique even less, and it didn't seem to help
much.

It looked like there might be something useful under the Associated Types
section of the type erasure documentation, but I couldn't quite figure it
out.

Any assistance would be most helpful.

Thanks,

-sc