redefine the policy for `lib::SeveralBuilder` to be a template-template parameter.
In fact it should have been this way from start, yet defining this kind of
very elaborate code bottom-up lets you sometime miss the wood for the trees
So to restate: `lib::SeveralBuilder` takes a ''policy template,''
which then in turn will be instantiated with the same types `I` (interface)
and `E` (element type) used on `SeveralBuilder` itself. Obviously, there can be
further types involved and thus additional type parameters may be necessary,
notably the ''Allocator'' — yet these are better injected when ''defining''
the policy template itself.
The default binding for this policy template is defined as `allo::HeapOwn`,
which causes the builder to allocate the storage extents through the standard
heap allocator, and for the created `lib::Several` to take full ownership of
embedded objects, invoking their destructors when falling out of scope.
Ichthyostega
1705c40dc2