require 'gtk2'

alias e puts

# Gdk::Display exists in ruby-gtk2:
pp Gdk::Display
pp Gdk::Display.class
e '='*80
e
e 'Does this method exist: Gdk::Display.default'
e
pp Gdk::Display.default # .primary_monitor.geometry.width
e '='*80
e 'Next testing Gdk::Screen.default:'
e
_ = Gdk::Screen.default
pp _
pp [_.width, _.height]

e '='*80
    
# The next method will fail for ruby-gtk2:
# pp Gdk::Display.default.primary_monitor.geometry.width