Re: Implicit Instantiations - was: Re: Why is Ada NOT a good choice for a beginner to programming?

[kcline17@hotmail.com (Kevin Cline)]

Richard Riehle <richard@adaworks.com> wrote in message news:<3E23A88A.2C0969B0@adaworks.com>...
> "Grein, Christoph" wrote:
> 
> > It is true, there are some places in Ada where implicit declarations or type
> > conversions are done, but implicit instantiations are as yet nowhere.
> 
> Implicit type conversions, along with implicit type promotions run
> counter to the Ada philosophy.

> C++ does not provide the same kind of capability for declaring new
> numeric types one has in Ada.   This, in spite of the entertaining
> example from Mr. Rosen.

C++ doesn't provide them explicitly.  But writing classes which
mimic Ada's numeric types is not difficult.  The C++ philosophy
is generally not to add features to the language which can be easily 
provided by a library.
 
> The whole idea of Ada is to declare types so they will be checked by
> the compiler and so mismatches will be caught.   If there is a problem
> with that, in the current standard, it needs to be fixed, but implicit
> conversions or promotions is simply a bad idea for this language.

No one wants implicit conversions or promotions.  But implicit 
instantiation of generic types would aid the development of type-safe code.

> Actually, I don't think there is really a problem here wrt Ada, even
> after reading your paper.

Given that strong type checking was a main goal in Ada's design, I think
Ada's inability to do compile-time validation of computations
involving physical units should be considered a rather serious flaw
in the language.