Perl 6 and Parrot Essentials, Second Edition

Methods

PIR provides syntax to simplify writing methods and method calls. These calls follow the Parrot-calling conventions. The basic syntax is similar to the single-line subroutine call above, but instead of a subroutine label name it takes a variable for the invocant PMC and a string with the name of the method:

object."methodname"(arguments)

The invocant can be a variable or register, and the method name can be a literal string, string variable, or method object register. This tiny bit of code sets up all the registers for a method call and makes the call, saving and restoring the top half of the register frames around the call. Internally, the call is a callmethodcc opcode, so it also generates a return continuation.

This example defines two methods in the Foo class. It calls one from the main body of the subroutine and the other from within the first method:

.sub _main
  .local pmc class
  .local pmc obj
  newclass class, "Foo"        # create a new Foo class
  find_type $I0, "Foo"         # find its dynamic type number
  new obj, $I0                 # instantiate a Foo object
  obj."_meth"( )               # call obj."_meth" which is actually
  print "done\n"               # "_meth" in the "Foo" namespace
  end
.end

.namespace [ "Foo" ]          # start namespace "Foo"

.sub _meth method             # define Foo::_meth global
   print "in meth\n"
   $S0 = "_other_meth"        # method names can be in a register too
   self.$S0( )                 # self is the invocant
.end

.sub _other_meth method       # define another method
   print "in other_meth\n"    # as above Parrot provides a return
.end                          # statement

Each ...