If anything that uses P::RD turns out to be faster than my( $x, $y, $z ) = @_;, it will indeed be "magic". Oh! and I'll eat my hat! (I'll have to buy a hat to eat, but I'm sure I can find something tasty at a thrift shop:)
To clarify, what I meant by my request for less overhead, was a reduction in the internal (C-level) overhead associated with calling a perl subroutine, that results in this kind of comparison of similar subroutines coded in Perl and another bytecode compiled, interpreted language: Java.
Are Perl's function calls slow?
The archetypal test of function call performance is the Ackermann Function. Go here to see the list of other languages that out-perform Perl for function call performance. Many of those are fully pre-compiled languages. Many are not.
For comparison purposes, look at straight forward implementations in Perl, with the same in Java.
Devel::Declare lets you hook into the perl parser and create your own bits of syntax. It's a little bit like a source filter, except more magical with all the good, bad, and ugly that can entail.
Perl6::Signature's being P::RD-based is not material here. Once per function, at parse time, Perl6::Declare will parse the Perl 6 signature of a sub and install data binding (and possibly, runtime checks) as appropriate.
The speed comes from another module (sorry to keep calling rabbits out of hats, those aren't the ones anyone gets to eat). It's Data::Bind, which too lacks documentation except for its tests. Word is it's in some cases faster than = @_.