Runtime type selection

[xorque <xorquewasp@googlemail.com>]

Hello.

I'd like to develop a program that processes a graph. The contents of
the graph are a random selection of objects of different types (all
elements may be of the same type or may all be different - assuming
there are enough types defined). By 'type' in this case, I am
referring
to Ada types.

The basic problem is that I want to create an object of a type picked
at
random, at runtime. I'm not entirely sure what my options are here.

I could create a base tagged type and derive a set of types from that
base, selecting at random. I could use variant records. It seems that
in
either case, I'd need to create an enumeration type with a 1:1 mapping
between enumeration values and derived types.

Both of these solutions seem a little unwieldly. They also seem like
they'd end up making the program difficult to extend (I'd ideally just
like to derive a new type and have it automatically available to be
selected at random for the graph).

Any ideas would be appreciated. I appreciate the problem is a little
abstract...