Suppose I have a class with a default attribute
class Foo { has Int $.a = 1; }
Now I want to write a custom constructor for it, with either `Foo.new()` or
`Foo.new(3)` doing the obvious thing. Here's one way to do it:
multi method new(Int $a = 1) { self.new(:$a); }
but this duplicates the default. Here's another:
multi method new() { self.new; }
multi method new(Int $a) { self.new(:$a); }
but this becomes horrible outside of the trivial cases.
I'm wondering if there's an idiomatic way to handle this without
duplicating the default. I think what I really want is something that says
"if $a is defined, then pass the named argument :$a; otherwise, pass
nothing". Something along the lines of
self.new(:a($a // Slip))
would be pretty good, except that Slip doesn't work like that, at least not
currently.
Another way to solve the same problem might be something like
multi method new(Int $a = Foo.^defaults<$a>) { self.new(:$a); }
if there was an easy way to access a class's variable defaults. (Is there
one that I don't know of?)
This isn't necessarily a big deal - right now I'm happy to just duplicate
my defaults - but it seems like something that's going to be a minor
annoyance in a lot of places.
