Hi. I was wondering why the following works:

    filter!(a => a % 2 == 0)(map!(a => a + 1)([1,2,3,4,5]))

but the following does not:

    [1,2,3,4,5]
        .map!(a => a + 1)()
        .filter!(a => a % 2 == 0)()

...giving me the error `Error: no property 'filter' for type 'Result'`

The dot syntax works fine if I'm just doing one map/filter/etc., though. Is
there a better way to do chaining like this? Am I misunderstanding how the dot
syntax sugar works or how map/filter/etc work in D? I'd prefer not to use the
first style as it can get a bit unwieldy...

Thanks for your time!
~DH

On Thursday, 12 April 2012 at 17:00:37 UTC, DH wrote:
> Hi. I was wondering why the following works:
>
>     filter!(a => a % 2 == 0)(map!(a => a + 1)([1,2,3,4,5]))
>
> but the following does not:
>
>     [1,2,3,4,5]
>         .map!(a => a + 1)()
>         .filter!(a => a % 2 == 0)()
>
> ...giving me the error `Error: no property 'filter' for type 'Result'`
>
> The dot syntax works fine if I'm just doing one map/filter/etc., though. Is
> there a better way to do chaining like this? Am I misunderstanding how the dot
> syntax sugar works or how map/filter/etc work in D? I'd prefer not to use the
> first style as it can get a bit unwieldy...
>
> Thanks for your time!
> ~DH

It works for the first argument because UFCS (that is, calling free functions as members) works for arrays but not for other types (ranges in this case) in DMD <=2.058.  Thanks to the intrepid Kenji it works for all types in the upcoming 2.059. You can try out the 2.059 beta here: http://ftp.digitalmars.com/dmd2beta.zip  Your second example should work fine in it.

Regards,
Brad Anderson

On Thu, Apr 12, 2012 at 07:00:35PM +0200, DH wrote:
> Hi. I was wondering why the following works:
> 
>     filter!(a => a % 2 == 0)(map!(a => a + 1)([1,2,3,4,5]))
> 
> but the following does not:
> 
>     [1,2,3,4,5]
>         .map!(a => a + 1)()
>         .filter!(a => a % 2 == 0)()
> 
> ...giving me the error `Error: no property 'filter' for type 'Result'`
> 
> The dot syntax works fine if I'm just doing one map/filter/etc., though. Is there a better way to do chaining like this? Am I misunderstanding how the dot syntax sugar works or how map/filter/etc work in D? I'd prefer not to use the first style as it can get a bit unwieldy...
[...]

The second syntax requires dmd 2.059, which is currently on beta. Earlier versions of dmd do not support this syntax.


T

-- 
Two wrongs don't make a right; but three rights do make a left...