In case it helps, I ran six versions of the OP's original program on Linux, with results shown below:

# Ran this little test program on Linux with perl -v printing:
# This is perl 5, version 40, subversion 0 (v5.40.0) built for x86_64-
+linux

use v5.40.0;
use feature 'class';
use experimental 'class';

class Gear {
   field $chainring :param :reader;
   field $cog :param :reader;
   field $rim :param :reader;
   field $tire :param :reader;

   method ratio {
      return $chainring/$cog;
   }

   method gear_inches {
      # this one failed:
      # Can't locate object method "ratio" via package "self"
      # return (self->ratio() * $rim) + ($tire * 2);

      # this one also failed:
      # Can't locate object method "ratio" via package "self"
      # return (self->ratio * $rim) + ($tire * 2);

      # this one worked, printing: 125.909090909091
      # return ($self->ratio * $rim) + ($tire * 2);

      # this one also worked, printing: 125.909090909091
      return ($self->ratio() * $rim) + ($tire * 2);

      # this one failed:
      # Cannot invoke method "ratio" on a non-instance
      # return (ratio() * $rim) + ($tire * 2);

      # this one failed:
      # Can't use string ("26") as a symbol ref while "strict refs" in
+ use
      # return (ratio * $rim) + ($tire * 2);

      # update: this one, suggested by [hippo]++, also works
      # return $self->ratio * $rim + $tire * 2;
    }
}

say Gear->new(chainring=>52, cog=>11, rim=>26, tire=>1.5)->gear_inches
+;
[download]

See Also

• Re: 5.40 released (perl new feature References)

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