Re: Attempting to modify a function result

["Robert I. Eachus" <eachus@mitre.org>]

"Raymond C. Rawa" wrote:
  
> I've encountered a "feature" of Ada83 or the VADS compiler that I don't
> understand.

   It is a feature of Ada, not just VADS.

>    ...Display.a := 5; -- I mean't to type: The_Display.a := 5;
 
   Display is a function that returns an object of type Display_Type. 
Display.a is a compontent of that object of type Integer, which gets
assigned the value 5.  What is hard about that?

> The procedure Foo.Huh compiles and executes without error.  As a side
> note, The_Display is unchanged by this procedure.

   That probably means that the function is returning a copy of
The_Display.  Some other implementation might return The_Display by
reference, in which case The_Display would be changed.
 
> Can someone please explain what's going on here?

   A function call can be the prefix of an indexed or selected
component, or even a slice.  In this case since Display has no
parameters, it surprised you.
(Actually I often use the construct of slicing the string returned by an
attribute: Put(Integer'Image(Foo)(2..Integer'Image(Foo)'Last); if I want
to drop the leading space.)
-- 

                                        Robert I. Eachus

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