"Darin Adler" a écrit dans le message de news:
B586F909-89D7-11D6-9349-0003935B80A2@bentspoon.com...
On Thursday, June 27, 2002, at 06:38 AM, Jean Llorca wrote:
Here upcasting means casting a base class to a derived class, I know
it may seem strange, bust boost offers a downcast
which does the static_cast the language does implicitly already (check
).
I think you've got it backwards. Downcasting, in Boost at least, means
casting a pointer to a base class part of an object to a pointer to a
derived class part of the same object. The polymorphic_downcast is
*not* doing a static_cast for a conversion the language already does
implicitly.
template
inline Target polymorphic_downcast(Source* x
BOOST_EXPLICIT_DEFAULT_TARGET)
{
assert( dynamic_cast<Target>(x) == x ); // detect logic error
return static_cast<Target>(x);
}
Sorry about it, but it's here in the code. This is in the last version of
the CVS. It does a static_cast. The compiler does static_cast implicitly in
some cases.
For instance a C++ compiler replaces the assert line with:
assert( dynamic_cast<Target>(x) == static_cast<Target>(x) );
Could you give a specific complete example (a file that would compile,
with all the declarations) of how one would use what you're proposing
to help make this clearer?
I enclosed two files to this reply. Don't scream about chosen class names
and stuff in the example ;)
begin 666 test.cpp
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