Re: C/C++ programmer giving Ada95 a chance -- writing an emulator.

[Geoff Bull <gbull@acenet.com.au>]

Tucker Taft wrote:
> 
> Geoff Bull wrote:
> >
> > If I Initialise the array like so:
> >
> >    Op_Table : array (Opcode) of Op_Root
> >      := (0 => Op_Root (O0),
> >          others => OU);
> >
> > then make the assignments:
> >     Op_Table (1) := Op_Root (O1);
> >     Op_Table (2) := Op_Root (O2);
> >     Op_Table (3) := Op_Root (O3);
> >

> >
> > What is going on here?
> > It look like the assigments throw away the tag (like Cohen
> > says it should) but the initializer keeps the tag.
> 
> That would be a bug.  The tag is *not* determined by the initial
> value if the target type is "specific" (as opposed to classwide).

> 
> Definitely a bug.  It looks like GNAT is copying the tag from the initial value,

I worked out exactly what is happening.
The bug is in aggregate assignments to an array or a record
of tagged components. I.e. I can later change the tags
in Op_table by making an aggregate assignment to it.

Also, if I don't initialise Op_table, it seems the tags in it are 
not initialised either. This seems wrong to me too, but I am just
guessing in this case.

Geoff