Intended behavior of automatic decimal point (bug 120940)
Eric Siegerman
pub08-gnc at davor.org
Thu Jul 27 21:27:45 EDT 2017
On Thu, Jul 27, 2017 at 08:20:50AM +0000, David T. via gnucash-devel wrote:
> I think of the decimal placement as applying to the final number in the field
> (as a sort of edit mask, if you will), rather than a preprocessing function
> that would apply to every element in an equation.
I'm not sure that would quite work either.
Currently, for simple numbers with no arithmetic, "1000" gets
auto-decimal-pointed ("scaled" hereafter), but "4.50" doesn't,
which are both just what one wants. The same should apply in
formulas (I think! -- but more about that at the end). Assuming
two auto-decimal places, consider:
1000 + 4.50
I (think I) want the first term to get scaled, but not the
second, giving a result of 14.50.
OK, so how about we scale each term separately, so that:
1000 * 3 + 450 -> 34.50
but also:
1000 * 3 + 4.50 -> 34.50
("->" meaning "yields a result of", since "=" just looks wrong
under the circumstances :-) ).
But then:
10.00 * 3 + 4.50 -> 34.50
We didn't want to scale the first term after all.
I've thought of a couple of different approaches:
- scale each term's resulting value if the term only contains
integers:
1000*3 + 4000 -> 30 + 40 = 70.00
1000*3 + 4000. -> 30 + 4000 = 4030.00
1000*3. + 4000 -> 3000 + 40 = 3040.00
1000*3. + 4000. -> 3000 + 4000 = 7000.00
- scale each term's *first* number if it's an integer,
but never second or subsequent numbers:
1000 * 3 -> 30
1000 * 3. -> 30
1000. * 3 -> 3000
1000. * 3. -> 1000
This is based on the thought that ($20 * $3) is meaningless;
it only makes sense to multiply money by something that isn't
money
But neither of those works in all situations.
The easiest way out, I think, is to never scale formulas at all,
only simple numbers. So:
4000 -> 40.00 # as currently happens
40. -> 40.00 # likewise
But:
4000+1 -> 4001.00
That's how my truly ancient copy of Excel behaves. (I don't
have access to a modern one.)
Or perhaps: for formulas, scale the final result (as you say),
but only if *all* of the numeric values the user typed are
integers:
1000*3 + 4000 -> 70.00
1000*3 + 4000. -> 7000.00
1000*3. + 4000 -> 7000.00
1000.*3 + 4000 -> 7000.00
That could boil down to:
Scale the final result unless the original input string
contains any "."s (or ","s depending on locale)
(without even any need to worry whether it's a number or
a formula).
But given that it's not entirely clear how even a simple:
1000 + 4.50
should behave, anything with any subtlety at all is going to want
a fair amount of testing to see whether people actually find it
usable. So an unsubtle approach like "never scale formulas" is
probably the safest place to start.
- Eric
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