How to pimp Scala collections with my own generic `map` (the right way)?

(By "get it to work with implicits" I mean "get it to work with
Arrays, Strings, and other types that can be viewed as collections.)

On Mon, Dec 12, 2011 at 6:22 PM, Yang Zhang wrote:
> This was originally posted to SO - any hints?
>
> http://stackoverflow.com/questions/8472654/how-to-pimp-scala-collections...
>
> I think dcsobral's answer comes close but we can't figure out how to
> get it to work with implicits.
>
> Also, would hugely appreciate anything in the way of English explanations.

2011/12/12 Yang Zhang :
> This was originally posted to SO - any hints?
>
> http://stackoverflow.com/questions/8472654/how-to-pimp-scala-collections...
>

This might help:

http://stackoverflow.com/questions/3225675/can-i-pimp-my-library-with-an...

2011/12/12 Carlos López Camey :
> 2011/12/12 Yang Zhang :
>> This was originally posted to SO - any hints?
>>
>> http://stackoverflow.com/questions/8472654/how-to-pimp-scala-collections...
>>
>
> This might help:
>
> http://stackoverflow.com/questions/3225675/can-i-pimp-my-library-with-an...

retronym's answer too falls short, and it furthermore assumes a higher
kinded type.

scala> Array(1).mapmap(1+)
:15: error: value mapmap is not a member of Array[Int]
Array(1).mapmap(1+)
^

scala> "hello".mapmap(x=>x)
:15: error: value mapmap is not a member of java.lang.String
"hello".mapmap(x=>x)
^

2011/12/12 Yang Zhang <yanghatespam@gmail.com>

retronym's answer too falls short, and it furthermore assumes a higher
kinded type.

scala> Array(1).mapmap(1+)
<console>:15: error: value mapmap is not a member of Array[Int]
             Array(1).mapmap(1+)
                      ^

scala> "hello".mapmap(x=>x)
<console>:15: error: value mapmap is not a member of java.lang.String
             "hello".mapmap(x=>x)
                     ^

I haven't tested it, but have you tried using '<%' instead of '<:'?
implicit def conv[A,C <% GenTraversable[A]](xs: C with GenTraversableLike[A,C])
--
Derek Williams

On Mon, Dec 12, 2011 at 7:40 PM, Derek Williams wrote:
> 2011/12/12 Yang Zhang
>>
>> retronym's answer too falls short, and it furthermore assumes a higher
>> kinded type.
>>
>> scala> Array(1).mapmap(1+)
>> :15: error: value mapmap is not a member of Array[Int]
>>              Array(1).mapmap(1+)
>>                       ^
>>
>> scala> "hello".mapmap(x=>x)
>> :15: error: value mapmap is not a member of java.lang.String
>>              "hello".mapmap(x=>x)
>>                      ^
>>
>
> I haven't tested it, but have you tried using '<%' instead of '<:'?
>
> implicit def conv[A,C <% GenTraversable[A]](xs: C with
> GenTraversableLike[A,C])

That doesn't work either.

On Mon, Dec 12, 2011 at 7:52 PM, Yang Zhang wrote:
> On Mon, Dec 12, 2011 at 7:40 PM, Derek Williams wrote:
>> 2011/12/12 Yang Zhang
>>>
>>> retronym's answer too falls short, and it furthermore assumes a higher
>>> kinded type.
>>>
>>> scala> Array(1).mapmap(1+)
>>> :15: error: value mapmap is not a member of Array[Int]
>>>              Array(1).mapmap(1+)
>>>                       ^
>>>
>>> scala> "hello".mapmap(x=>x)
>>> :15: error: value mapmap is not a member of java.lang.String
>>>              "hello".mapmap(x=>x)
>>>                      ^
>>>
>>
>> I haven't tested it, but have you tried using '<%' instead of '<:'?
>>
>> implicit def conv[A,C <% GenTraversable[A]](xs: C with
>> GenTraversableLike[A,C])
>
> That doesn't work either.

Guess I might as well paste:

scala> implicit def conv[A,C <% GenTraversable[A]](xs: C with
GenTraversableLike[A,C])
| = new { def mymap[B,D](f: A => B)(implicit b:
CanBuildFrom[C,B,D]): D = b(xs).result // placeholder
| }
conv: [A, C](xs: C with
scala.collection.GenTraversableLike[A,C])(implicit evidence$1: C =>
scala.collection.GenTraversable[A])java.lang.Object{def mymap[B,D](f:
A => B)(implicit b: scala.collection.generic.CanBuildFrom[C,B,D]): D}

scala> List(1) mymap (_+1)
res0: List[Int] = List()

scala> Array(1) mymap (_+1)
:15: error: value mymap is not a member of Array[Int]
Array(1) mymap (_+1)
^

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Am 13.12.2011 03:22, schrieb Yang Zhang:

We don't "pimp" any more, we "enrich" now. ;)

On Mon, Dec 12, 2011 at 8:58 PM, Stefan Wagner wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Am 13.12.2011 03:22, schrieb Yang Zhang:
>
> We don't "pimp" any more, we "enrich" now. ;)

Duly noted. :)

Here is something that almost works:
implicit def conv[A, C[_]](xs: C[A])(implicit ev: C[A] => GenTraversable[A]) = new {  def mymap[B,D](f: A => B)(implicit cbf: CanBuildFrom[C[A],B,D]): D = {     ...  }}
It works with Arrays, but it doesn't work with Strings.
--
Derek Williams

Here's another version, which doesn't work as an implicit, but I have no
idea why:

implicit def conv[A, Coll]
(xs: Coll)(implicit ev: Coll => TraversableLike[A, Coll]) = new {

def foo[B, That]
(f: A => B)(implicit cbf: CanBuildFrom[Coll, B, That]) = null

}

scala> Array(1,2,3).foo(_.toString)
:15: error: No implicit view available from Array[Int] =>
scala.collection.TraversableLike[A,Array[Int]].
Array(1,2,3).foo(_.toString)

However:

scala> conv(Array(1,2,3)).foo(_.toString)
res1: Null = null

On Tue, Dec 13, 2011 at 12:21 AM, Lars Hupel wrote:
> Here's another version, which doesn't work as an implicit, but I have no
> idea why:
>
> implicit def conv[A, Coll]
>  (xs: Coll)(implicit ev: Coll => TraversableLike[A, Coll]) = new {
>
>    def foo[B, That]
>      (f: A => B)(implicit cbf: CanBuildFrom[Coll, B, That]) = null
>
> }
>
> scala> Array(1,2,3).foo(_.toString)
> :15: error: No implicit view available from Array[Int] =>
> scala.collection.TraversableLike[A,Array[Int]].
>              Array(1,2,3).foo(_.toString)
>
>
> However:
>
> scala> conv(Array(1,2,3)).foo(_.toString)
> res1: Null = null
>

This one was also in my original SO question :)

> This one was also in my original SO question :)

Yours were slightly different -- the first one used `<:<` instead of
`=>` which doesn't work if you have an implicit conversion; and the
second one used `GenTraversable` which doesn't work for non-generic
collections. But yes, it suffers from exactly the same problems.

On 2011-12-13 9:21, Lars Hupel wrote:
> Here's another version, which doesn't work as an implicit, but I have no
> idea why:

Probably due to https://issues.scala-lang.org/browse/SI-3346

-sz

On Tue, Dec 13, 2011 at 00:22, Yang Zhang wrote:
> This was originally posted to SO - any hints?
>
> http://stackoverflow.com/questions/8472654/how-to-pimp-scala-collections...
>
> I think dcsobral's answer comes close but we can't figure out how to
> get it to work with implicits.
>
> Also, would hugely appreciate anything in the way of English explanations.

Yang, at the time I tried to find a link without success, but I just
found it: https://gist.github.com/257758

This shows type bounds, and explains a bit the difference between
them. It won't help you with what you want, but you had questions
about this too. :-)