A Hash object which raises an error if any previously-defined key attempts to be set again.
foo = Hash::Static.new foo['name'] = 'Tom' #=> 'Tom' foo['age'] = 30 #=> 30 foo['name'] = 'Bob'
produces
ArgumentError: Duplicate key for StaticHash -- 'name'
StaticHash has it's orgins in Gavin Kistner's WriteOnceHash class found in his basiclibrary.rb script.