FROGGS/unposal.md

## unposal.md

      
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              unposal.md
            
          
    my @items := nqp::unpack( 'U2 (xxxC)[W]', $binary_string );
I, FROGGS, solemnly propose the implementation of pack() and unpack in nqp.
For one, these are useful for Perl 5 and Perl 6, and the other reason is that they should be pretty fast.
If a backend then can even provide a faster implementation (e.g. in C), then it would be easy to #ifdef it in.
The signatures I propose are:
my $str  := nqp::pack( "CCC", [65, 66, 67] );
my @list := nqp::unpack( "CCC", $str );
You might wonder how this will cope with Buf, Str, utf8 and what not. Since pack/unpack work on byte-level,
and one must be able to extract a single byte of a utf8-byte-sequence, it gets a string of octets.
class utf8
    multi method unpack(utf8:D: $template) {
        nqp::unpack( $template, nqp::decode(self, 'ascii') );
    }
}
Implementaion details

I would implement it exactly like nqp::sprintf, because unpack supports group-repeatition and relative
positioning inside groups.
What needs to be discussed is how diretives like I should be handled. I'd like to see some sort of dynamic variable, a hash,
which can be set to specify how many bytes a native int should have when packing it into a string.
Same technique would be useful for sprintf's platform specific directives.