Re: Decimal: Formal review begins.

From: Alexander Grund (alexander.grund_at_[hidden])
Date: 2025-01-20 10:16:35

Am 18.01.25 um 12:48 schrieb Christopher Kormanyos via Boost:
> > Could you illustrate such a use case?
> > Concretely, what do you mean by
> > several widths of types? Do you
> > mean decimal32 vs decimal64?
> Yes. Let's say you made a program
> that uses one data table for a type T that could be decimal32, 64 or 128.
> But you only wanted one table.
> You would make the table entries with the highest width suffix and decoratee ach table entry with a static-cast to T in order to get all the table entries into type T.
> To be fair, everyone already has todo something like this with normal float, double and long double.
>> With the syntax you have today,
>> you already have distinct suffixes
>> for each type (i.e. _df always constructs
>> decimal32, _dd always constructs decimal64,
>> and so on).
> Yes. And I gave one potential recipe on how to deal with this in generic code above. My judgement may have been hurried and might seem unfair.
> But my intuition tells me, a whole bunch of clients would run into compilation failures. Until they come up with their own recipes for generic literal values.
> And the result would be more frustration than had we simply done nothing.
I'm not sure I understand this.
How can you have "generic code" with different suffixes where there are 
compilation failures that would not be there in non-generic code?
 From "one data table for a type T" I imagine something like

`T table[] = {1.25_df, 3.2_df, 51_df}`

So while your table type is generic the constants used are not.
If the above errors due to using `1.25352397826723672375_df` you ought 
to use `_dd` to be able to use it in `decimal64 table[]` anyway.
I don't see a scenario where it would be ok to truncate a constant and 
then store them in a type that would have been able to store the 
nun-truncated value.
The other way round is more reasonable to use rounding/truncation when 
really required by the target type.

Can you explain which case you had in mind?