The closest to null is actually an undefined type object On Mon, Dec 28, 2020, 3:36 PM yary <not....@gmail.com> wrote:
> Been thinking about this, and checked out the Rakudo repository to peek > into the source. > > Allowing Failure as a return always makes sense to me– every block needs > to be capable of passing along a failure, that's how the language is > designed. > > On the other hand, Nil is not a Failure. Conceptually it is a lack of an > answer, similar to SQL's null concept. > > What's the usefulness of having Nil skip return type checking- > specifically Nil and not its Failure descendents? > > This example under https://docs.raku.org/type/Nil shows what I think is a > less-than-awesome specification, and I am curious about the reasoning > behind it being defined as valid > > sub a( --> Int:D ) { return Nil } > > > > -y > > > On Sun, Dec 20, 2020 at 7:18 PM Brad Gilbert <b2gi...@gmail.com> wrote: > >> Nil is always a valid return value regardless of any check. >> >> This is because it is the base of all failures. >> >> On Sat, Dec 19, 2020, 8:17 PM yary <not....@gmail.com> wrote: >> >>> Is this a known issue, or my misunderstanding? >>> >>> > subset non-Nil where * !=== Nil; >>> (non-Nil) >>> > sub out-check($out) returns non-Nil { return $out } >>> &out-check >>> > out-check(44) >>> 44 >>> > out-check(Nil) >>> Nil >>> >>> ^ Huh, I expected an exception on "out-check(Nil)" saying the return >>> value failed the "returns" constraint. >>> >>> The subtype works as I expect as an the argument check >>> >>> > sub in-check (non-Nil $in) { $in } >>> &in-check >>> > in-check(33) >>> 33 >>> > in-check(Nil) >>> Constraint type check failed in binding to parameter '$in'; expected >>> non-Nil but got Nil (Nil) >>> in sub in-check at <unknown file> line 1 >>> in block <unit> at <unknown file> line 1 >>> >>> $ raku --version >>> This is Rakudo version 2020.07 built on MoarVM version 2020.07 >>> implementing Raku 6.d. >>> >>> Is this my understanding of return type checking that's off, or a known >>> issue, or something I should add to an issue tracker? >>> >>> -y >>> >>
