[boost] Re: Yet another Variant class

From: Itay Maman (itay_maman_at_[hidden])
Date: 2002-07-01 23:34:57

David Abrahams wrote:
 > Oh, this is spooky. I am just implementing similar functionality in v2 of
 > the Boost.Python library. In v1 it was called from_python.
 >
 > The problem: a Python object (usually managed via a PyObject*, but in
 > Boost.Python managed with the wrapper class object) can in principle hold
 > any C++ type. A major component of the Boost.Python library's 
functionality
 > is the extraction of C++ objects from Python objects, and the wrapping of
 > C++ objects into Python objects.
 >
 > So, should I call my from_python function variant_cast<> as well? I don't
 > think that reads well. In particular, I think of a cast as generally 
being
 > a peer-to-peer type transformation, whereas these "casts" are
 > container-to-containee transformations. I was thinking of "extract":
 >
 >     extract<int>(obj)
 >
 > Now, "extract<>" might be too-general a name to use in namespace 
boost, but
 > I'm not sure that it is. I do think it works better than 
"variant_cast<>".
 >
 > Thoughts?
 > Dave
 >

The Inheritance relationship is also a composition. So, the upcast of a
class D to its base class B, may also be referred to as 'extracting' B
out of D. Nonethless, this primitive is widely known as casting.

I think the same logic should be applied here: Althought we are actually
extracting a held value, we may still use 'variant_cast' to describe the
operation.

-Itay