array << hoge || default

hoge.rb

require "pp"
require "ripper"

pp Ripper.sexp("arr << nil || 1")
# =>
# [:program,
#  [[:binary,
#    [:binary,
#     [:vcall, [:@ident, "arr", [1, 0]]],
#     :<<,
#     [:var_ref, [:@kw, "nil", [1, 7]]]],
#    :"||",
#    [:@int, "1", [1, 14]]]]]

pp Ripper.sexp("arr.<< nil || 1")
# =>
# [:program,
#  [[:command_call,
#    [:vcall, [:@ident, "arr", [1, 0]]],
#    :".",
#    [:@op, "<<", [1, 4]],
#    [:args_add_block,
#     [[:binary,
#       [:var_ref, [:@kw, "nil", [1, 7]]],
#       :"||",
#       [:@int, "1", [1, 14]]]],
#     false]]]]

pp Ripper.sexp("arr.push nil || 1")
# =>
# [:program,
#  [[:command_call,
#    [:vcall, [:@ident, "arr", [1, 0]]],
#    :".",
#    [:@ident, "push", [1, 4]],
#    [:args_add_block,
#     [[:binary,
#       [:var_ref, [:@kw, "nil", [1, 9]]],
#       :"||",
#       [:@int, "1", [1, 16]]]],
#     false]]]]