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Re: .kv ?

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From:
Simon Proctor
Date:
September 14, 2018 11:03
Subject:
Re: .kv ?
Message ID:
CAGwa-jjAPPvNSzd8SioH+4r18+tSRtkGwy6opeE2nrpfRecN1g@mail.gmail.com
:D is a type constraint requiring an instantiated (or defined) object of
the given type (or a subtype of it).

:U is a type constraint saying you have a container specified for the given
type that hasn't been instantiated.

So if you have my Int $a; you have said this should hold and Int but it's
currently valueless (undefined). It would match Int:U in a signature.

Assign 5 to it and it's now defined and matches Int:D in a signature.

On Fri, 14 Sep 2018, 11:44 Todd Chester, <ToddAndMargo@zoho.com> wrote:

> >> On Fri, 14 Sep 2018, 11:22 Todd Chester, <ToddAndMargo@zoho.com
> >> <mailto:ToddAndMargo@zoho.com>> wrote:
> >>
> >>     Hi All,
> >>
> >>     I adore the "kv" method:
> >>
> >>     $ p6 'for "abc\n23\n4.56".lines.kv -> $i, $j { say "$i  $j" };'
> >>     0  abc
> >>     1  23
> >>     2  4.56
> >>
> >>     So, I decided to go and look at:
> >>     https://docs.perl6.org/routine/kv
> >>
> >>     multi method kv(Any:U:  -->List)
> >>     multi method kv(Any:D:  -->List)
> >>
> >>
> >>     Okay, here is what I see:
> >>
> >>     "method"  is .foo style of a routine
> >>
> >>     "Any:U:" and "Any:D:" are what goes in front of .foo
> >>     and it can be of type "Any".
> >>
> >>     https://docs.perl6.org/type/Any
> >>
> >>            ":D" mean constrained, meaning it much have something
> >>
> >>            What is ":U"?
> >>
> >>            Whatever ":U", how can it be both?
> >>
> >>     The second ":" is the delimiter for what goes in front of the .foo,
> >>     meaning it has finished its declaration of what that in front is.
> >>     Kind of like a comma.
> >>
> >>     "-->List" mean something is returned of type "List"
> >>     https://docs.perl6.org/type/List
> >>
> >>            0  abc
> >>            1  23
> >>            2  4.56
> >>
> >>
> >>     How have I done so far?
> >>
> >>
> >>     And is there a list somewhere of the meanings of ":U" and ":D"
> >>     and such so the next time I see one that I do not recognize,
> >>     I can look it up?
> >>
> >>     Many thanks,
> >>     -T
> >>
>
>
> On 09/14/2018 03:28 AM, Simon Proctor wrote:
> > :D means a defined value. So it's when you have an instance. :U is
> > undefined so it's when you call kv as a classethod.
> >
> > Pair.kv would be :U.
> > (A => "b").kv would be :D
> >
> >
>
> Hi Simion,
>
> I am not following.  What do you mean by "undefined"?
>
> I can't make head or tails out of "Pair"
> https://docs.perl6.org/type/Pair
>
> I thought ":D" meant "constrained"?
>
> Yours in confusion ,
> -T
>

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