[swift-evolution] Still Missing: Fixed Decimal Numerical Type.

[Michael Gottesman]

+CC Steve

> On Mar 30, 2016, at 6:09 AM, Ted F.A. van Gaalen via swift-evolution <swift-evolution at swift.org> wrote:
> 
> There is still no fixed decimal numerical type available in Swift!
> 
> It should be  implemented *as soon as possible* 
> because the fixed decimal type is really needed 
> for applications working with financial and statistical data!
> 
> E.g. 
> var depositPromille: Decimal(10,3) = -1234.56
> typealias  Money = Decimal(20,2) 
> 
> Important: Implementation should be on a low level
> and must be very, very efficient!
> This is because usually in financial applications 
> very large amounts of data (e.g. bank accounts) are processed. 
> 
> I’d suggest that Swift could deploy already existing
> Fixed Decimal library functions available. 
> In fact, many do exist, for example here:
> http://gcc.gnu.org/onlinedocs/gcc-4.6.0/libstdc++/api/a01152.html <http://gcc.gnu.org/onlinedocs/gcc-4.6.0/libstdc++/api/a01152.html> 
> 
> Of course, the fixed decimal type is also available in most relational databases,
> currently there is no 1:1 way to get this type of data   DB <—> Swift,
> and to process it easily in Swift. One now has to convert it e.g.
> to large integers, thereby also somehow remembering the decimal fraction.
> Yes, one could write a class/struct for it, but one also has
> to implement all the arithmetic involved, with also needs 
> rounding, truncation, etc. It would also be too slow.
> 
> For those still considering using floating point types
> for this purpose e.g. Double: Forget it, because 
> floating point types don’t have the required exact precision.
> E.g. € 234,565,098.01   // the one cent at the end is important!
> 
>   
> For some idea  on how this could be implemented in the Swift language
> please read a PL/1 manual, like this one: 
> 
> http://www.ibm.com/support/knowledgecenter/#!/SSY2V3_4.3.0/com.ibm.entpli.doc_4.3/lr/preface_plugin.htm <http://www.ibm.com/support/knowledgecenter/#!/SSY2V3_4.3.0/com.ibm.entpli.doc_4.3/lr/preface_plugin.htm>
> 
> especially under sub-topic “Data elements” 
> 
> 
> 
> Kind Regards
> TedvG
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