Re: Need advice re package organization.

["Robert I. Eachus" <rieachus@attbi.com>]

Stephen Leake wrote:

> The core tool is probably best written in Ada using ASIS; it would be
> somewhat similar to Auto_Text_IO. Emacs ada-mode and GPS could provide
> user interfaces to the tool, but it would really need to be run as
> part of the build process (from a makefile).
> 
> Hmm. That would imply that the inquiry functions where in a child
> package; no problem if they don't need to be dispatching.

You made me think for a while, but I came back to my original idea.  The 
problem with automatically generated non-dispatching inquiry functions 
would be that, when overloading occurs, the user is going to be really 
upset by the lack of a class-wide operation.  The easiest way to explain 
it is that inserting a type conversion to a specific type would get the 
code to compile, but sometimes that conversion would raise an exception 
at run-time.  So, I don't see problems occuring frequently, if your 
design is the more typical bushy Ada style derivation tree, but I see 
them as nasty when they arise.

So I think it is much better to have the inquiry functions in the 
package which declares the type, which seems to rule out ASIS as a 
generator, unless the ASIS package generated as set of inquiry functions 
for the type and all types derived from it.  This might require multiple 
child packages to be generated.  A typical inquiry function might look like:

    function Selling_Price (Stock_Item'Class) return Dollars;

And the ASIS tool would have to generate explicit dispatching code in 
the body, with the appropriate with clauses.

I think that is probably overkill for inquiry functions, but it might 
work well for things like creating a model-view-controller environment 
with on screen display for things like bench testing subsystems.  The 
test environment could automatically be generated from the software and 
a test script.  (The test script would provide the inputs and a list of 
the objects to be displayed.)


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