Array#uniq - Comparison doesn't use 'eql?' and 'hash'

I am confused about "Array#uniq". In it is described, that one has to redefine "eql?" and "hash", if one needs an own "Array#uniq" interpretation.

I made tests with the result, that neither "eql?" nor "hash" is called. What went wrong here?

>>>>> code >>>>>

class String
   alias :org_hash :hash
   alias :org_eql? :eql?
   def hash
     puts 'String#hash called'
   def eql?(other)
     puts 'String#eql? called'

puts 'Start of test'
a = ['a', 'b', 'a', 'c', 'b']
b = a.uniq
p b
puts 'End of test'

>>>>> Output >>>>>

Start of test
["a", "b", "c"]
End of test

>>>>> EoE >>>>>

Wolfgang Nádasi-Donner