In this case, `!$double` isn't a sigil. `!` is just the old prefix operator for negating a value [1]. If you meant to write `$!double`, then it's the twigil [2] for class attributes [3]. Twigils could be considered as secondary sigils but they affect the scoping of a variable. In this instance, `!` is for class attributes and will only be found there.
As for `.@sigils`, I've never seen this syntax. I'm probably out of the loop in this one.
As an aside, sigils are one of Raku's interesting features. They convey information [4] that might not be easy to discern from just looking at the code. What kind of structure is this variable holding? Is it holding an array? A hash? A code object? What's the scope of this variable? Is it class-scoped? Is it dynamically-scoped? Is it a compile-time variable?
> ... Raku is quite slow.
This is a legitimate reason for avoiding the language. However, it's worth pointing out that Raku core developers have made great improvements to the language in the speed department since it was first officially released in 2015. They recognize there's a lot of room for improvement. [5]
[1] https://docs.perl6.org/routine/!
[2] https://docs.perl6.org/language/variables#index-entry-Twigil
[3] https://docs.perl6.org/language/variables#index-entry-$!
[4] https://docs.perl6.org/language/faq#Why_sigils?_Couldn't_you...?
[5] https://docs.perl6.org/language/faq#Is_Perl_6_fast_enough_fo...?
