Hallo Michael,
Du schriebst am Wed, 13 Nov 2013 13:01:42 +0100:
> > The "with" construction is well optimized by complilers.
> A decent compiler can do the same optimization even without being hinted
> to do so by the programmer's using "with"
Yes, with enough implementation effort on the side of the compiler, it can.
> > Also without"with" we'll have C-ish nightmare with long chained OOP
> > idents.
> You can use intermediate variables instead, making (IMHO) the code much
> less ambiguous and not much more blurred.
A decent compiler can do the same optimization even without being hinted
to do so by the programmer's using intermediate variables.
Indeed, a strongly optimizing compiler might insert intermediate variables
in many places where the programmer didn't think of doing so, and can remove
such when the programmer meant them to convey some important information.
BTW, intermediate "variables" (I suppose you're thinking of _pointer_
variables here) are very similar to the Oberon-style "with" Martin
suggested, they're implicitly declared such variables. And that's why I
don't really like them - instead of "opening" the direct access to the
fields of a record, it requires you to use an alias name, a nickname for
the real variable. Indeed, their handling is very similar to the usage of
nicknames for people in some restricted group - if you leave the group, you
better not use the nickname, as no one recognizes it outside, it might even
be detrimental or at least cause confusion. The same appiles to these
intermediate variables, either declared (and assigned) explicitely or by
the Oberon-style "with" construct.
> BTW.:
> I vote for the possibility to define local variables anywhere and not
> just before the first begin of a function.
That's a completely different thing with an ability to cause confusion.
In addition, it simply doesn't fit any Pascal style syntax, not even the
older Algol style.
Algol _did_ provide block local variables within enclosing blocks, though -
it just didn't allow them to be defined "anywhere". Algol, like Pascal,
uses separation of declarations and statements, and it did so also for
theses variable declarations. I'm not sure any more, and I cannot refer to
any documentation right now, but I think the syntax looked somewhat like
the normal procedure syntax, just without a header. I.e.:
VAR { global declarations }
... { declarations }
BEGIN { outermost block }
... { statements }
VAR { block local declarations }
... { declarations }
BEGIN { interior block }
... { statements }
END;
... { statements }
END;
where the block local declarations are only valid within the interior
block, while the global declarations (and any declarations from blocks
fully enclosing the interior one) are visible also as long as they're not
overridden by more local ones, as usual.
(And, as an additional bonus, Algol even allowed to use block external
variables in the declaration of block local ones, even for array boundaries
and such things.)
BTW, there are additional issues with local variables that make them
sometimes rather intransparent in C: if the languages provides for
preinitialization of variables, how are the initial values handled if a
local block gets executed repeatedly? C requires the compiler to generate
code to implicitely reinitialize them every time, as long as they're real
_local_ variables and not declared "static", what makes them global and
initialized only once on program startup.
Delphi only initializes them once and makes initialized variables always
"C static", i.e. global, although just locally visible. There are other
possibilities, but all except the "globalizing" approach need hidden code
generation by the compiler. This might be considered unwanted.
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Mit freundlichen Grüßen, S. Schicktanz
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