Programming Perl, 4th Edition

Overloading Constants

You can change how constants are interpreted by Perl with overload::constant, which is most usefully placed in a package’s import method. (If you do this, you should properly invoke overload::remove_constant in the package’s unimport method so that the package can clean up after itself when you ask it to.)

Both overload::constant and overload::remove_constant expect a list of key/value pairs. The keys should be any of integer, float, binary, q, and qr, and each value should be the name of a subroutine, an anonymous subroutine, or a code reference that will handle the constants.

sub import { overload::constant ( integer => \&integer_handler,
                                  float   => \&float_handler,
                                  binary  => \&base_handler,
                                  q       => \&string_handler,
                                  qr      => \&regex_handler ) }

Any handlers you provide for integer and float will be invoked whenever the Perl tokener encounters a constant number. This is independent of the constant pragma; simple statements such as:

$year = cube(12) + 1;        # integer
$pi   = 3.14159265358979;    # float

will trigger whatever handler you requested.

The binary key lets you intercept binary, octal, and hexadecimal constants. q handles single-quoted strings (including strings introduced with q) and constant substrings within qq- and qx-quoted strings and here documents. Finally, qr handles constant pieces within regular expressions, as described at the end of Chapter 5.

The handler will be passed three arguments. The first argument is the original constant, in whatever form it was provided ...