> On 21 Oct 2025, at 09:23, ToddAndMargo via perl6-users <[email protected]>
> wrote:
>
> On 10/20/25 10:28 AM, Quanrong via perl6-users wrote:
>> > Oh, but it *does* serve a purpose, and it *will* fire under the right
>> > circumstances! For instance:
>> >
>> > $ raku -e 'sub a(--> Int:D) { Int }; a'
>> > Type check failed for return value; expected Int:D but got Int (Int)
>> > in sub a at -e line 1
>> > in block <unit> at -e line 1
>> You are right! I had missed that, it's very obvious in retrospective. Now I
>> understand.
>> Thanks for your help! And for working on Raku :)
>
>
> Okay, made me look up what an Int:D is. This back
> from search.brave.com's AI:
>
> In Raku, Int:D refers to a type constraint that specifies
> a defined value of the Int type. It is used to restrict
> a variable or parameter to only accept instances of the
> Int class (i.e., actual integer values), excluding the
> Int type object itself. For example, declaring
> my Int:D $x = 42;
> ensures that $x can only hold an integer value and not
> the Int type object. This constraint is useful for enforcing
> that a variable contains a concrete, defined integer rather
> than a type object. The :D smiley stands for "definite,"
> indicating that the value must be defined.
>
> I use Int a lot. When would Int:D be useful? When you
> want the finger wagged at you if you send a Nil?
>
> Yours in confusion,
Well, you could want it when you want to make sure something gets initialized:
$ raku -e 'sub a(--> Int:D) { my Int $b; $b }; a'
Type check failed for return value; expected Int:D but got Int (Int)
in sub a at -e line 1
in block <unit> at -e line 1
