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From: Noah Roberts (roberts.noah_at_[hidden])
Date: 2007-03-27 17:33:25

Michael Fawcett wrote:
> On 3/26/07, Martin Schulz <Martin.Schulz_at_[hidden]> wrote:
>> B) The presentation layer consists of everthing that is visible to the
>> user, namely the GUI or the like. People in academics can hardly imagine
>> what expectations engineers might have towards the units of their data.
>> (Before entering industry, I was no exception to that rule :-) ) This
>> is partly due to historical reasons; the choice of units in the
>> presentation layer may vary by corporate guidelines, personal
>> preference, professional background of the user or geographical
>> location. If you want to get around with a single piece of code then,
>> you cannot live with a fixed units for the quantities in your program.
>> (The presentation layer, that is -- computation kernels are another
>> story.)
> I'm a little unclear on why some people think run-time support is
> required for robust interaction with GUIs. It could very well be a
> misunderstanding on my part, but with a user interface that allows
> arbitrary units, wouldn't you still need something like this:
> // Assume quantity<abstract> provides run-time support
> quantity<abstract> on_dialog_ok()
> {
> int selection = get_combobox_selection(ID_COMBO_DISTANCE);
> double value = get_editbox_value<double>(ID_EDIT_DISTANCE);
> quantity<abstract> distance;
> // This must be kept in sync with the dialog resource
> switch (selection)
> {
> case Meters:
> distance.reset(distance * meters);
> break;
> case Feet:
> distance.reset(distance * feet);
> break;
> // etc
> }
> return distance;
> }

Nope. Your dialog manager would keep track of the unit and set
appropriately upon initialization and/or user interaction. Your reader
would then be as simple as setting the value directly to the quantity.
Alternatively you might have something like this:

quantity<abstract> on_dialog_ok()
   quantity<abstract> dist;

No more switch statement smell.

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