$ bin/console
tapioca(main):001> require "google/protobuf/well_known_types"
=> true

# initialize takes an Array
tapioca(main):003> fm = Google::Protobuf::FieldMask.new(paths: ["a", "b"])
=> <Google::Protobuf::FieldMask: paths: ["a", "b"]>
tapioca(main):004> fm.paths
=> ["a", "b"]
tapioca(main):005> fm.paths.class
=> Google::Protobuf::RepeatedField

# initialize with RepeatedField fails
tapioca(main):006> Google::Protobuf::FieldMask.new(paths: fm.paths)
(tapioca):6:in 'Google::Protobuf::AbstractMessage#initialize': Expected array as initializer value for repeated field 'paths' (given Google::Protobuf::RepeatedField). (ArgumentError)
        from (tapioca):6:in 'Class#new'
        from (tapioca):6:in '<top (required)>'
        from <internal:kernel>:168:in 'Kernel#loop'
        from bin/console:13:in '<main>'

# attr writer with Array fails
tapioca(main):010> fm.paths = ["a", "b"]
(tapioca):10:in 'Google::Protobuf::AbstractMessage#method_missing': Expected repeated field array (Google::Protobuf::TypeError)
        from (tapioca):10:in '<top (required)>'
        from <internal:kernel>:168:in 'Kernel#loop'
        from bin/console:13:in '<main>'

# attr writer takes RepeatedField
tapioca(main):014> fm.paths = Google::Protobuf::RepeatedField.new(:string, ["b", "c"])
=> ["b", "c"]
tapioca(main):015> fm.paths.class
=> Google::Protobuf::RepeatedField
tapioca(main):016> fm.paths
=> ["b", "c"]