Re: [Seed7-users] Dynamic dispatch strange behaviour

[Thomas M. <tho...@gm...>]

"Leonardo Cecchi" <leo...@gm...> wrote:
> I was reading the new manual chapter (it's the chapter I was looking
> for) I discovered a strange issue.
> I don't know if it's a bug but I can't explain to myself the behaviour
> of the following program:
> 
> $ include "seed7_05.s7i";
> 
> const type: strangeInterface is new interface;
> const func string: getNome(in strangeInterface param) is DYNAMIC;
> 
> const type: astronave is new struct
>   var string: nome is "";
> end struct;
> type_implements_interface(astronave, strangeInterface);
> 
> const func astronave: astronave(in string: nome) is func
>   result
>     var astronave: result is astronave.value;
>   begin
>     result.nome := nome;
>   end func;
> 
> const func string: getNome(in astronave: a1) is func
>   result
>     var string: result is "";
>   begin
>     result:=a1.nome;
>   end func;
> 
> const proc: main is func
>   local
>     var strangeInterface: enterprise is astronave("Enterprise galactica");
>   begin
>     writeln("one");
>     writeln("the name:" & getNome(enterprise));
>     writeln("two");
>   end func;
As far as I can see you discovered a bug.
It has to do with the initialisation of interface
variables. When you change the 'main' program to
 const proc: main is func
   local
     var strangeInterface: enterprise is astronave("Enterprise galactica");
   begin
     enterprise := astronave("Enterprise galactica");
     writeln("one");
     writeln("the name:" & getNome(enterprise));
     writeln("two");
   end func;
it works (at least for me). Does it work for you?

I have not investigated more about the bug than that.
It is obvious that I need to revise the initialisation
of interface variables. In the meantime it is
necessary to assign a value with := to an interface
variable.

There is more to revise in this area:
It can happen that several interface variables
point to one implementation value. Since this is
sometimes desired and sometimes not I may move
to the use of an explicit 'new' function.

What do you think?

Greetings Thomas Mertes

Seed7 Homepage:  http://seed7.sourceforge.net
Seed7 - The extensible programming language: User defined statements
and operators, abstract data types, templates without special
syntax, OO with interfaces and multiple dispatch.

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