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From Jochen Theodorou <blackd...@gmx.org>
Subject Re: Casting Double to BigDecimal
Date Tue, 12 Jan 2016 00:39:08 GMT

Well, cheap and fast is of course relatively spoken ;)

Anyway... the general path is ScriptBytecodeAdapter.castToType. But in 
many cases we do actually emit direct code for transformation, if we 
have enough information to do that.

As of why asType uses the toString path... that would be 
https://issues.apache.org/jira/browse/GROOVY-3171 not sure if the reason 
is really valid though I must say... someone is always surprised and I 
don't know if newbies will us "as"

bye Jochen


Am 11.01.2016 um 15:48 schrieb Alberto Vilches:
> Interesting! now I have more doubts about this:
>
> 1 Where is this cheap & fast implementation of the Java-like casting? Is
> it in GDK or it is implemented at low-level by the Groovy compiler? I
> only know the asType method in DefaultGroovyMethods.
> 2 Why the "asType" method use the expensive way new
> BigDecimal(d.toString()) instead the fast?
>
> Thank you Jochen. :)
>
> On Mon, Jan 11, 2016 at 2:00 PM, Jochen Theodorou <blackdrag@gmx.org
> <mailto:blackdrag@gmx.org>> wrote:
>
>     We tryied to have two different kinds of casts. The normal one, that
>     is more in the style of Java, which tries the cheapest way. And the
>     "as" version, which calls into asType is customizable and usually
>     does more expensive operations. The fallback for asType is the
>     normal cast. That's why we see asType as an extended cast. But don't
>     expect asType simply as something that allows for more cases than
>     the normal cast. I can have different conversion logic.
>
>     Now
>
>     new BigDecimal(d)
>
>     is much cheaper than
>
>     new BigDecimal(d.toString())
>
>     That those two do not match is actually because of d.toString(),
>     which does simply give 1.9 here, instead of the exact double value.
>     That this toString() methods behaves in this way has not always been
>     the case afaik.
>
>     bye Jochen
>
>     Am 11.01.2016 um 10:57 schrieb Alberto Vilches:
>
>         Yes, I know the "1.9" literal in Groovy results in a BigDecimal.
>         That's
>         why I'm trying to force the double using the "d", but maybe is
>         still a
>         bigdecimal. So, let's try again:
>
>               Double d = 1.9
>               println((BigDecimal)d)
>
>         prints "1.899999999999999911182158029987476766109466552734375"
>
>         and
>
>               Double d = 1.9
>               println d as BigDecimal
>
>         prints "1.9"
>
>
>
>         On Fri, Jan 8, 2016 at 1:34 PM, Naresha K. <naresha.k@gmail.com
>         <mailto:naresha.k@gmail.com>
>         <mailto:naresha.k@gmail.com <mailto:naresha.k@gmail.com>>> wrote:
>
>              Value 1.9 will be of type BigDecimal.
>              Why are you using D?
>
>
>              On Fri, Jan 8, 2016 at 5:45 PM, Alberto Vilches
>         <vilches@gmail.com <mailto:vilches@gmail.com>
>              <mailto:vilches@gmail.com <mailto:vilches@gmail.com>>> wrote:
>
>                  Hi everybody! We have an issue in our application, and we
>                  realized these two lines have differents results. We
>         wonder why
>                  because we think it should calls to the
>                  DefaultGroovyMethods.asType(Number self, Class<T> c).
>         But it
>                  seems only the explicit call to "as" finally calls to
>         the asType
>                  and the casting do a different thing (just a new
>                  BigDecimal(1.9D), but we wonder in which part of Groovy is
>                  happening)
>
>                  (BigDecimal)1.9D  //
>                  "1.899999999999999911182158029987476766109466552734375" ->
>                  1.9D as BigDecimal  // "1.9"
>
>                  In fact, we tried to put these two lines in the Groovy
>         console
>                  and see the AST in all the phases. But in all of them
>         shows the
>                  same code:
>
>                      public java.lang.Object run() {
>                           ((1.9) as java.math.BigDecimal)
>                           return ((1.9) as java.math.BigDecimal)
>                       }
>
>                  Somebody please could give some light? Thank you very
>         much and
>                  happy new year :)
>
>                  --
>                  Un saludo.
>                  Alberto Vilches
>
>
>
>
>
>         --
>         Un saludo.
>         Alberto Vilches
>
>
>
>
> --
> Un saludo.
> Alberto Vilches

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