Re: Ada Successor Language

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2018-06-19 22:30, Paul Rubin wrote:
> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>> Generics and macros are same thing regardless implementation.
> 
> I don't understand what the issue is.

1. Generics is a second-order language. We don't need yet another 
language unless strong reasons shown. [ This how Stepanov's advocacy 
goes. He tries to show that generic programming requires generics. My 
point is that maybe not. ]

2. Generics are static. There is no class-wide instances of generic 
classes. E.g. taking the generic class "(<>) is private" as in

    type T is (<>) is private;

There is no way to declare:

    X : (<>) is private'Class := <result from some instance>;

This has very concrete consequences. For example, declare dimensioned 
measurement unit types in a generic and then try to write a calculator 
dealing with units. No way.

3. Once generic, always generic.

4. No proper reuse. Generic bodies are no proper compilation units, you 
cannot have a shared library of generics. Therefore the only possible 
form of reuse is textual substitution and recompilation of the client code.

5. No proper separation of interface and implementation. If you used Ada 
generics you would know that successful compilation of a generic body 
means little. Instantiation can always fail even if all formal 
parameters match. The compiler must look into the body not just for the 
sake of optimization and representation, but for validity of 
instantiation, just like in C++. A macro is a macro.

> I don't think it was a mistake
> for C++ to have generics since the generic approach in C++ is IME much
> better than the OO approach with inheritance.

This is evidently wrong. Ada programs extensively using generics are as 
impossible to maintain as C++ programs using templates. IMO generics 
have no place in SW engineering.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de