Re: [BLACKBOX] IN Parameters - Making the design more regular

From: [at]} <Chris>
Date: Wed, 30 Jan 2008 15:52:25 +1030

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>-----Original Message-----
>From: BlackBox [mailto:BLACKBOX{([at]})nowhere.xy
>Sent: Tuesday, 29 January 2008 5:04 AM
>To: BLACKBOX{([at]})nowhere.xy
>Subject: Re: [BLACKBOX] IN Parameters - Making the design more regular
>
>Hi all,
>
>I can not see real advantages in the proposed change. There
>may under circumstances be some with respect to clarity of
>sourcecode when a procedure-parameter (RECORD, ARRAY, INTEGER,
>CHAR, BOOLEAN or whatever
>else) is declared as IN-parameter (remember all of them may be
>OUT-parameters anyway).

Exactly. Consistency can be very helpful in reducing confusion when learning
/ using a language.

>On the other side it must be clear that IN-parameters in the
>first line were not introduced for the purpose of clarifying
>source code. The idea, as far as I know, when introducing the
>keyword IN for RECORDs and ARRAYs was to avoid substantial
>amounts of allocating and deallocating of memory
....
....

That is certainly part of the story. Have a look at the section 'IN and OUT'
in BlackBox > Help > What's New for a good description of the motivation
behind the design.

>... every VAR-(IN-)parameter
>invokes an extra pointer, that is 4 bytes, and the necessary
>detours through memory at run time.
....
>But exactly this will be reintroduced into
>Component Pascal when parameters like (IN xyz: CHAR) are
>allowed.

I'm not sure that I understand what you are saying. I'm not proposing that
non-structured IN parameters are handled in the same way as VAR parameters.
That only should be the case for records and arrays. The way I have
implemented it is that

  (IN xyz: CHAR)

is implemented *identically* to

  (xyz: CHAR)

as far as memory allocation etc. goes.

The only difference is that xyz is subsequently subject to the same
compile-time checks as it would be if defined as a read-only variable:

VAR
  xyz-: CHAR;

>The slight improvement this might have on the source
>code level in my opinion is not worth the above mentioned run
>time drawbacks.

Does now knowing that such runtime drawbacks do not exist change your
opinion?

Thanks for taking to time to respond,

Chris Burrows
CFB Software
http://www.cfbsoftware.com/cp

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Received on Wed Jan 30 2008 - 06:22:25 UTC