Perl 6 Deep Dive

Example of using the gist method

For the user-defined classes, it is possible to create a gist method that prepares the output as desired. Let us try this on the following example.

We create a class for storing chemical formulae. The goal is to allow creating a chemical formula in pure ASCII format and then print it so that numerical indices are displayed as subscripts.

class Chemical {
    has $.formula;
    method gist {
        my $output = $!formula;
        $output ~~ s:g/(<[0..9]>)/{(0x2080+$0).chr}/;
        $output;
    }
}

The Chemical class has a data member $.formula, which keeps the original ASCII formula as a string. The gist method converts it to a string with subscripts. We make a replacement using regular expressions. Regular expressions are covered in detail ...