Re: An Ada9X mimic of C++ friends?

[comar@cs.nyu.edu (Cyrille Comar)]

jhoward@solar.sky.net (John Howard) writes:
: designer who anticipates future use; or, it requires the user must have 
: access to the underlying code so that it can be changed.  Both of these 
: are poor assumptions."
: 
: I am new to Ada.
: So my question is: does the explicit use of "TAGGED" in Ada95 have the same 
: negative consequences as specifying "virtual"?

Being obliged to specify "virtual" in C++ is not 100% negative. It has
an impact on code generation (a non-virtual function call is more
efficient than a virtual function call).

Anyway the Ada95 approach is different. All subprograms defined
"reasonably close to the type definition" (I won't try to give the
formal definition here :-) are primitive, i.e. virtual in the C++
sense and can be overridden by descendants. In the other hand the
notion of Class-Wide type (which doesn't exist in C++) allows the
compiler to know if the  call to a primitive operation is dispatching
or not so you only pay for dispatching when you actually use it. I
have been told that some C++ compilers were able to optimize calls to
virtual functions that are obviously not dispatching but the C++
typing mechanism doesn't give much room for this kind of
optimizations...
 
-- 
------------------------------------------------------------------------
Cyrille Comar,                                  E-mail: comar@cs.nyu.edu
Gnat Project                                    US phone: (212) 998-3489