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Set by lizmat on 8 June 2022.
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stevied why does a `multi method new()` method get called with `Object.new(foo => 'buzz')` 18:44
Nahita perhaps because of the %_ 18:45
a method takes arbitrary number of named parameters by default
to ease inheritance stuff 18:46
stevied huh, didn't know that. what is %_?
Nemokosch Is it the only candidate that gets called? 18:47
stevied no, I have other multi new method if that's what you mean
Nemokosch Yes 18:48
Nahita it gets the extra named parameters into itself in methods implicitly
in normal subroutines it doesn't appear
stevied ok, I see it here: docs.raku.org/language/functions#A...signatures 18:49
Nahita somewhat akin to @_ getting the positional arguments into itself *if* it's explicitly referred within the body of a routine
well in Perl that's the only way of getting implicitly the parameters
except they have introduced signatures recently... finally...
well you know Perl better than me so 18:50
Nemokosch Well, are they used though
stevied so here's the new method I have: 18:51
```
multi method new() {
self.bless(dir => $*CWD);
}
```
how do I catch if a bad named arg is passed?
Nemokosch I'd say it's quite bizarre that named arguments can be discarded like that...
stevied I gotta check %_ I guess? 18:52
Nahita well you can explicitly check whether %_ is empty
but there are 2 more ways actually
one is marking the class as `is hidden`
as mentioned, %_ exists for "interface consistency"
like to redirect methods to parents in children
with whatever args they passed 18:53
with `class A is hidden { }`, you kill that redispatching mechanism
depending on what's wanted, that might or might not be okay
other solution is to do `*% ()` in the signature of the method 18:54
that says "take *any* number of extra named parameters such that they are destructable to... well nothing!"
so it will prevent any extra arguments if that makes sense
maybe there are other ways idk 18:55
stevied huh, interesting
Nahita the % parameter is unnamed but it can be named like `*%a ()` but since the purpose of its existence there is something different, i.e., prevent extras, it might as well be unnamed to signal that 18:57
and language fantastically allows unnamed parameters, so
stevied so I got this: 18:58
```
multi method new(*%) {
self.bless(dir => $*CWD);
}
```
that still allows me to do `new(zzz => 'fuzz')`
oh, wait, read your wrong
ok, works: `*% ()` 19:00
weird though. don't quite get it
Nemokosch Tbh you would almost think this should be the default behavior...
Nahita `*%` means: slurp *every* extra named parameter you can right? 19:01
`*%h` means: slurp *every* extra named parameter you can right?
like `*@a` means slurp every positional
lizmat indeed
stevied what is the `()` though?
lizmat and that is always implicit in method signatures
Nemokosch Perhaps if a missing signature weren't mistaken for an empty signature, the right thing would happen by default
Nahita that's the destructuring part
that's so cool actually 19:02
it applies not only the hashes but arrays too
Nemokosch <@563790557831495691> you pointed out the inconsistency accurately, by the way: a subsignature doesn't quite work like the signature itself 19:03
I hope I have that issue somewhere...
Nahita an example
```py
>>> sub f(@arr ($first, *@rest)) { $first.say; @rest.elems.say }
>>> f ["head", 10, 20, 30]
head
3
```
an example 19:04
```perl
sub f(@arr ($first, *@rest)) {
$first.say;
@rest.elems.say
}
>>> f ["head", 10, 20, 30]
head
3
```
this is an "extension" of `sub f(@arr)` of writing things
i'm expecting a positional allright
and i also destructure it along the way for use in the subroutine
$first and the *@rest 19:05
stevied jesus, I got some more learning to do, I guess
Nahita i can do `Int $first` there
and all of a sudden i have a requirement that the passed array need its first element to be Integer
so wrapping up with the *% ()
stevied yeah, I see now 19:06
Nahita i want everything, anything named to be captured
stevied cool
Nahita ok
stevied the requriement is it's empty
Nahita yeah :p
everything and nothing
stevied I didn't know about that "extension" syntax. probably read it, made no sense to me, so I forgot it 19:07
signatures in raku are GD insane compared to perl. never seen anything like it before. does any language do such similar gymnastics? 19:08
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Nemokosch Oh right, I found the issue 19:31
you can pass a pair to a function like a named argument, or like a positional argument 19:32
so far so good
how can you pass it like a positional argument, if you have a subsignature?
and the pair should be a part of the subsignature
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