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Content-type: text/plain
Stan,
I like the idea of Named Integers. They would indeed simplify the
documentation (now, what possible problems could they cause?).
-Doug
Stan Warford wrote:
> The benefit of named integers is self-documentation. On the surface,
> they look like enumerated types, but they are fundamentally different
> because they do not have the implementation problems of type
> checking that enumerated types have. Hence, you get 90% of the
> benefits of enumerated types with 10% of the implementation cost.
>
> Here is an example. In the documentation for Module Ports, we have
>
> CONST
> invert = 0; hilite = 1; dim25 = 2; dim50 = 3; dim75 = 4;
>
> Then, later in the documentation we have
>
> (f: Frame) MarkRect (l, t, r, b, s: INTEGER; mode: INTEGER; show:
> BOOLEAN), NEW;
>
> Then, still later in the documentation, we have this explanation
>
> CONST invert, hilite, dim25, dim50, dim75
> These values may be passed as mode-parameter to procedure MarkRect.
>
> The parameter list of MarkRect is _not_ self-documenting. All you know
> by looking at formal parameter mode is that it is an integer. All you know
> by looking at the CONST section is that there are some integer constants,
> but you have no way of knowing which of the integer constants, if any,
> is meant to be used as the mode value in MarkRect. You must search through
> the documentation for the explanation.
>
> Named integers would work like this.
>
> TYPE
> MarkMode = (invert, hilite, dim25, dim50, dim75);
>
> (f: Frame) MarkRect (l, t, r, b, s: INTEGER; mode: MarkMode; show:
> BOOLEAN), NEW;
>
> Although the syntax looks like the syntax of enumerated types, named
> integers are _not_ enumerated types. As I understand it, 90% of the
> difficulty of implementing enumerated types is the type checking that must
> occur across modules. The implementation difficulty was so severe that
> enumerated types were not included in the definition of CP.
>
> Named integers have none of the implementation problems of enumerated
> types. They are simply a syntactic sugar that provide an immense benefit
> of self-documentation for a very small price. They do not introduce a new
> type. Named integers _are_ integers. In general
>
> TYPE Alpha = (beta, gamma, delta);
>
> is _defined_ to be exactly equivalent to
>
> TYPE Alpha = INTEGER;
> CONST beta = 0; gamma = 1; delta = 2;
>
> As far as export is concerned
>
> TYPE Alpha* = (beta, gamma, delta);
>
> is defined to be equivalent to
>
> TYPE Alpha* = INTEGER;
> CONST beta* = 0; gamma* = 1; delta* = 2;
>
> There is no need for complex type-checking rules with enumerated values
> as there is in C++. gamma _is_ an INTEGER and can be used anywhere an
> integer can be used. mode is still an INTEGER. Named integers would change
> _nothing_ in the implementation of the entire BlackBox framework except for
> making the interfaces much easier to read.
>
> When I was first learning the BB framework I was used to software design
> that emphasized enumerated types for self-documentation. It was a source
> of irritation to see an integer parameter in a formal parameter list and
> not
> know immediately which set of integer constants applied to it. I think one
> reason it has been a hard sell to the folks at Oberon microsystems is that
> they are so familiar with the framework that they forget what it is like
> for
> a novice to be learning BB for the first time.
>
> Stan
>
> J. Stanley Warford
> Professor of Computer Science
> Pepperdine University
> Malibu, CA 90263
> Stan.Warford{([at]})nowhere.xy> 310-506-4332
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Received on Sun Nov 21 2004 - 02:39:04 UTC