gistfile1.rb

# gsub! doesn't return anything when no changes are made

irb(main):006:0> 'abc'.gsub('c','d')
=> "abd"
irb(main):007:0> 'abc'.gsub!('c','d')
=> "abd"
irb(main):008:0> 'abc'.gsub!('d','c')
=> nil

# It's usual usage pattern (working on an existing object) still works

irb(main):002:0> a = 'abc'
=> "abc"
irb(main):003:0> a.gsub! 'd',''
=> nil
irb(main):004:0> a
=> "abc"