Re: how do i implement double-dispatching?

[cl1motorsports <cwlambert76@yahoo.com>]

On Mon, 22 Dec 2003 17:49:41 -0500, Stephen Leake wrote:

> cl1motorsports <cwlambert76@yahoo.com> writes:
> 
>> Okay. now it works when the Visitor type, Visit() procedures and the
>> Accept_Visitor() procedure is in a separate package from the parse tree.
>> but when i try to combine the 2 into one package i get
>> an error about multiple dispatching on all of the Visit() procedures.
>> what is my scope issue with being in the same package that doesn't apply
>> to them being in 2 packages?
> 
> In general, you will find that the Ada rules encourage putting things
> in different packages. This is a Good Thing :).
But in this case there is no point of having a visitor with out a tree to
visit or a parse tree with no visitor to run operations on it. Currently
to use this in a program i have to do this:

with Parse_Tree_Pkg; use Parse_Tree_Pkg;
with Abstract_Visitor_Pkg; use Abstract_Visitor_Pkg;
with Interpret_Tree; use Interpret_Tree;

a person using the interpret_Tree package having to know that it's
created from an abstract visitor package exposes implementation and that's
what I am trying to avoid. The user should only have to do:

with parse_tree_pkg; use parse_tree_pkg;
with Interpret_Tree; use interpret_Tree;

am i correct on this or am i missing something?


> 
> Sometimes child packages work better.