On Wednesday, 4 September 2013 13:19:16 UTC+8, Mikera wrote:
> On Friday, 2 August 2013 12:28:51 UTC+8, CGAT wrote:
>
>> My understanding of == is that it is intended to establish numerical
>> equivalence
>> across types. But I think that basic contract fails with BigDecimal.
>> For instance,
>>
>> (== 1M 1.0M) ; => false
>>
>> because the scale properties of these numbers are different. So then of
>> course:
>>
>> [(== 1 1N 1.0) (== 1 1N 1.0 1M) (== 1 1N 1.0 1.0M) (== 1 1.0 1N 1.0M)]
>> ; => [true true true false]
>> and
>> [(== 1.0M 1.0) (== 1.0 1) (== 1 1N) (== 1N 1.0M)]
>> ; => [true true true false]
>>
>> I find your lack of transitivity (and commutativity) ... disturbing.
>>
>> The issue is that there are two notions of equality for BigDecimal,
>> equals and compareTo, where equals compares value *and* scale while
>> compareTo compares numerically.
>>
>> The other numeric types use equals for equivalence, quite reasonably.
>> But in class BigDecimalOps in clojure/lang/Numbers.java, I propose
>> that
>>
>> public boolean equiv(Number x, Number y){
>> return toBigDecimal(x).equals(toBigDecimal(y));
>> }
>>
>> should be
>>
>> public boolean equiv(Number x, Number y){
>> return toBigDecimal(x).compareTo(toBigDecimal(y)) == 0;
>> }
>
>
> Ouch, is that really what Numbers.equiv is doing?
>
> No wonder some of our idiomatic numerical code is so slow - a coercion to
> BigDecimal is really expensive!
>
> It really needs instanceof checks and branches to handle the different
> cases efficiently. I'll have a go at a ticket/patch that addresses this.
>
Sorry that was a false alarm, having looked at the source I see it's
checking for BigDecimal instances before this point, and dispatching to
different Ops instances as required.
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