[BLACKBOX] IN Parameters - Making the design more regular

From: [at]} <CFB>
Date: Tue, 29 Jan 2008 00:24:35 +1030

----boundary-LibPST-iamunique-831418065_-_-
Content-type: text/plain

I propose that the following section of Paragraph 10.1 of the Component
Pascal Language Report be replaced:

"There are two kinds of parameters, value and variable parameters, the
latter indicated in the formal parameter list by the presence of one of the
keywords VAR, IN, or OUT. Value parameters are local variables to which the
value of the corresponding actual parameter is assigned as an initial value.
Variable parameters correspond to actual parameters that are variables, and
they stand for these variables. Variable parameters can be used for input
only (keyword IN), output only (keyword OUT), or input and output (keyword
VAR). IN can only be used for array and record parameters. Inside the
procedure, input parameters are read-only."

The text to replace it would be:

"There are four kinds of parameters: value, input, variable and output
parameters. Value parameters are the default, the other kinds of parameter
are indicated in the formal parameter list by the presence of one of the
keywords IN, VAR, or OUT. Value and input (keyword IN) parameters are local
variables to which the value of the corresponding actual parameter is
assigned as an initial value. Inside the procedure, input parameters are
read-only. Variable and output parameters correspond to actual parameters
that are variables, and they stand for these variables. Variable parameters
can be used for output only (keyword OUT), or input and output (keyword
VAR)."

This change has the following benefits:

* The inclusion of IN and OUT keywords in Component Pascal was intended to
allow interface declarations to be made more precise and more
self-documenting. The presence of the IN keyword in the procedure heading is
a guarantee that the value of the parameter will remain constant throughout
the procedure. Parameters of any type - INTEGERs, CHARs, BOOLEANs etc. may
now also be guaranteed in this way. The potential benefits are no longer
strictly limited to records and arrays.

* The design is more regular tending to make it easier to comprehend.

* The existing ability to pass a string constant as an actual parameter to
an input character array is no longer a special case that needs an
exceptional explanation.


Note the following:

* Existing programs will still compile and run without change.

* The compiler developer is still free to implement efficient handling of
records and arrays when used as input parameters. As is the case currently,
such parameters do not need to be copied to the stack when the procedure is
invoked.

* Expressions, not just variables, may be passed as input parameters.
 
* The development effort to implement the changes is minimal. I have a
working experimental version of the BB 1.6rc5 compiler with modifications to
implement the changed design. In total, 2 lines of code were changed, 1 line
of code was added, and 1 line of code was removed.

If there is sufficient interest in this proposal I will do further, more
rigorous, testing and then make the code available. If anybody would like to
volunteer to help test it please let me know,

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

----
To unsubscribe, send a message with body "SIGNOFF BLACKBOX" to LISTSERV{([at]})nowhere.xy----boundary-LibPST-iamunique-831418065_-_-
Content-type: application/rtf
Content-transfer-encoding: base64
Content-Disposition: attachment; filename="rtf-body.rtf"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----boundary-LibPST-iamunique-831418065_-_---

Received on Mon Jan 28 2008 - 14:54:35 UTC