Re: status of Ada STL?

[Mark Biggar <mark.a.biggar@attbi.com>]

"Dmitry A. Kazakov" wrote:
> 
> procedure '':=" (Target : in out A; Source : A); -- (*)
> 
> Note I do not demand that the copy constructor would be derived from
> ":=". It is IMO a wrong idea to attempt to derive one from another.
> C++ does it simplier. What is actually wrong in C++ is that the result
> of "=" is not void.
> 
> >Wouldn't it also fall apart if we started including "+:="?
> 
> No, they should be just user-defined procedures. Whether they are
> primitive or not should only depend on the freezing rules and whether
> particular parameters are class-wide.
> 
> (*)  There is a minor problem with unconstrained subtypes passed as
> inout and that discriminants cannot be changed.

There are other problems as well.  This was looked at in detail during
the Ada95 revision.  Allowing users to redefine ":=" using a procedure
definition like that above was determine to be way too course grained.
Do you expect your new assignment operation to compose for record or 
array types? What about variable initialization?  Or, the assign out
during procedure exit for out parameters?

This is way ada95 controlled types are tagged and break the assignment
process down into finer parts with Initialize, Adjust and Finalize
as user definable hooks into a larger assignment process.  This way
use defines the type specific parts of data movement and the compiler
is free to use them in various ways to move data around in ways the 
guarantees that the type's data abstractions are preserved. 

--
Mark Biggar
mark.a.biggar@attbi.com