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

From: [at]} <Josef>
Date: Tue, 29 Jan 2008 12:58:10 +0100

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I agree with Robert that IN (as it is used by BB now)
is not the same as CONST (as it has been proposed by Wirth in Oberon-SA
http://www.cs.inf.ethz.ch/~wirth/Articles/OberonSAReport.pdf).

IN means that you are not allowed to change a VAR-parameter
inside the procedure, however it might be changed
outside the procedure by some side effect. Therefore it is not strictly
constant. It is sufficient for passing string literals by reference, and this
is probably the main application area.

IMHO the two concepts cannot be merged into one without breaking existing code.
Also, the benefit is marginal in my experience.

I doubt that Wirth allows the usage of const parameters in ConstExpression
as for example in the declaration of an array type inside a procedure.
This would sometimes be a useful feature, however, it may put large amounts
of data onto the stack and it is complicated to implement inthe compiler.
Java went the other way and tried to keep the stack small
by requesting to allocate arrays on the heap.

- JT

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Received on Tue Jan 29 2008 - 12:58:10 UTC