Re: Runtime type selection

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

xorque wrote:
> On Oct 11, 5:02 pm, Niklas Holsti <niklas.hol...@tidorum.invalid>
> wrote:
>> Keep a list or array of (accesses to) a factory function for each
>> possible (derived) type.
> 
> 'Lo,
> 
> That does sound like the sort of thing I'd have done in C.

Yes. Ada makes it easier since you can use elaboration-time statement 
blocks in package bodies to register stuff.

> I still
> have a nagging sensation that Ada actually provides other means to
> do this based on such things as the 'Tag attribute.

Did you read about the package Ada.Tags (RM 3.9)? There is a generic 
function Ada.Tags.Generic_Dispatching_Constructor that takes a tag as 
parameter and creates an object with that tag, but I don't hink there is 
any way to find the tags for all types in a given derivation class. So 
even with  Ada.Tags.Generic_Dispatching_Constructor your program still 
has to register the types, or their tags, or a prototype object of each 
type, to create the program-accessible set of types/tags that can be in 
the graph.

Perhaps some expert can explain why this reflection capability (find 
tags for all derived types in a class) was not included in Ada.Tags? 
Perhaps because Ada run-time systems do not need such a function for 
their own purposes?

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .