🚀 go-pugleaf

(A copy of this message has also been posted to the following newsgroups:
comp.std.c++)

In article <MATT.95Sep8112137@physics2.Berkeley.EDU>,
fjh@munta.cs.mu.OZ.AU (Fergus Henderson) wrote:

>> I already know that the static type of `dynamic_cast<T*>(p)' is `T*',
>> because `dynamic_cast<T*>(p)' is already part of standard C++.
>> What I am asking about is the static type of your newly proposed syntax
>> `dynamic_cast<bar>(foo)', where `bar' is a value of type type_info, not
>> a type.
>> 
>> I think your idea doesn't make sense, because there *isn't* any sensible
>> static type for that expression.  Since C++ is a statically typed language,
>> every expression must have a static type, but that expression can't have
>> one.  Therefore it doesn't work in C++.

The sensible static type for that expression will be a 'void*'.

I know this sounds ugly, but so does 'dynamic_cast<void*>(p)', which as
I'm sure you know, returns a pointer to the complete object, but in the
form of a void*.

The issue here is that one has the ability to 'cast-down' to the complete
object, using 'dynamic_cast<void*>(p)' ( meaning, without knowing the
complete type type) and getting a void*, but no ability to 'cast-up' ( an
implicit procedure in C++ ) without knowing the sub-type type at compile
time.

This is needed in the same cases it is needed when using the returned
pointer from 'dynamic_cast<void*>(p)', to do the inverse-operation.

Please look at another article of mine in this thread for a usage and an
implementation.

Etay.

-- Etay Bogner,
-- Etay_Bogner@mail.stil.scitex.com,
-- Scitex Corp.
-- Israel.
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