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

["Grein, Christoph" <christoph.grein@eurocopter.com>]

From: kcline17@hotmail.com (Kevin Cline)

> Grein writes:
> 
>   But the request to have full dimensional checking persists as can be seen
>   from the pertinent discussions in newsgroup Comp.Lang.Ada. There are two
>   basic ways one can try to solve the problem, either by adding to the
>   numeric value its dimension as attribute, or by using different types for
>   different dimensions.  Since the first method is runtime-consuming,
>   whereas the second one is only compiletime-consuming, all effort naturally
>   concentrates on the second method.   This is doomed to fail
>   as is shown in the paper cited above - although a plethora of overloaded
>   operations is used, the result is not really satisfactory.
>   Physical equations with all their powers and roots evade these attempts.
> 
> In short, Ada's requirement for explicit generic instantiation repels
> attempts to create a compile-time verified system of dimensional types,
> and Grein gave up on attempts to achieve compile-time type safety.
> 
> C++ does not have this problem, and compile-time type safety is
> achieved in a fairly obvious way.

This C++ feature pleases me so that I'm apt to wish something like it were 
available in Ada.

However I have not thought about all implications this would induce in 
connection with all other features in Ada, so this might turn out to be a kind 
of Pandora's box.

It is true, there are some places in Ada where implicit declarations or type 
conversions are done, but implicit instantiations are as yet nowhere.