the template lib::PolymorphicValue seemingly picked the wrong
implementation strategy for "virtual copy support": In fact it is possible
to use the optimal strategy here, since our interface inherits from CloneSupport,
yet the metaprogramming logic picked the mix-in-adapter (which requires one additional "slot"
of storage plus a dynamic_cast at runtime).
The reason for this malfunction was the fact that we used META_DETECT_FUNCTION
to detect the presence of a clone-support-function. This is not correct, since
it can only detect a function in the *same* class, not an inherited function.
Thus, switching to META_DETECT_FUNCTION_NAME solves this problem
Well, this solution has some downsides, but since I intend to rewrite the
whole virtual copy support (#1197) anyway, I'll deem this acceptable for now
TODO / WIP: still some diagnostics code to clean up, plus a better solution for the EmptyBase
Up to now, PolymorphicValue was always used as-is, packaged into a typedef.
Now we consider using it as building block within an adapter for visitor-like tokens.
Which requires to pass-down the ctor call directly from the subclass, at least if we
want to emplace the resulting entity directly into a stdlib container.
As an asside, PolymorphicValue also used explicit specialisations for N-arguments,
which meanwhile can be replaced by variadic templates
...which leads to a specific twist here; while in the simple version
we still could hope to get away with a simple uniform uint argument,
the situation has changed altogether now. The canvas has turned into
some generic component, since it is instantiated two times, onece for
the time ruler and once for the actual body content. Thus all of the
specifics of the drawing code need to be pushed into a new, dedicated
renderer component. And this more or less forces us to pass all the
actual presentation variations through the invocation arguments of
the visitor.
So we're now off again for a digression, we need a more generalised visitor
- default recommendation is to implement DiffMutable interface
- ability to pick up similar non-virtual method on target
- for anything else client shall provide free function mutatorBinding(subject)
PERSONAL NOTE: this is the first commit after an extended leave,
where I was in hospital to get an abdominal cancer removed.
Right now it looks like surgery was successful.
- we use a GenNode element
- this holds a polymorphic value known as DataCap
- besides simple attribute values, this may hold collections of GenNode sub elements
- a special kind of GenNode collection, the Record, is used to represent objects
The purpose of this setup is to enable an external model representation
which is only loosely coupled to the interndal data representation
through the exchange of (tree)diff messages
Previously, I've added an additional '&' to be able
to pass references without much ado. This turned out
to be problematic when using constant values at the
invocation site. Well. C++ has really a fixation
ont passing things by value. This is fine, but
doesn't play so well at times when passing smart-ptrs
or similar ref-counting stuff, especially when we just
want to *use* the handle, not store it away.
Essentially the same situation as with for_each
Bottom line: from now on, we need to state the
template parameter for such arguments explicitly,
or just accept the overhead of creating an additional
transient copy of the smart-ptr.
Using a policy based switch in case the client
interface collaborates and provides copy operations;
in this case, a direct static downcast instead of
the expensive indirect (dynamic) cast to the
management interface can be employed.
