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From: Mike Young <mikey@mcs.com>
Subject: Re: Something like "->" in Ada?
Date: 1996/04/02
Message-ID: <31620B5E.FCD@mcs.com>#1/1
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Date: 1996-04-02T00:00:00+00:00
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Robert Dewar wrote:
> 
> Chris says
> 
> "   I am learning OOP with Ada 95.  Although I have only a bit of experience,
> mostly with Perl 5, I find that the "->" operator is much more intuitive
> than passing an object as a parameter to a subprogram.  Is it possible to
> define "->" as the following:"
> 
> What you are used to always seems more intuitive than what you are
> getting used to. Wait till you can say "I have completely learned OOP
> with Ada 95", then see what you think. Many people think that the
> procdure argument approach is in fact much simpler, and that the ->
> is unnecssarily restrictive and over-specific.

=======
Mayhaps, Robert. I would appreciate any help you might offer.

In playing with Intermetric's adajava package last night, I had 
an interesting few minutes translating the following Java statement into 
Ada-ish code:

   (size().width - g.getFontMetrics().stringWidth(helloStr))

The Ada equivalents I finally coughed up are:

1) (size(this).width - stringWidth(getFontMetrics(G), hello_Str))

2) declare
     pSize : Rectangle_Ptr := size(this);
     fontM : FontMetrics_Ptr := getFontMetrics(G);
   begin
     ...
       (pSize.width - stringWidth(fontM, hello_Str)),
       ...
   end;

In other words:          g().f().func(...);
compares to:             func(f(g(this)), ...);

I'm not drawing any conclusions from this exercise, but the contrast 
between Java's cascading style and Ada's func(f(g(x)), ...) style 
appears somewhat extreme. The Java version is consistent with a 
heirarchy (g.getFontMetrics().stringWidth(...)); this has some value 
when trying to unravel what stringWidth is. Also, there's a certain 
inconsistency in inverting the relationship when an attribute is 
directly accessed, compared to calling functions only. Changing an 
attribute into a function call would involve more work in re-ordering 
the statement.

But, as you say, it's probably a matter of acclimation. 

Mike.