instance method compile_if_an_interpolation

# File activesupport/lib/active_support/vendor/i18n-0.4.1/i18n/backend/interpolation_compiler.rb, line 27
        def compile_if_an_interpolation(string)
          if interpolated_str?(string)
            string.instance_eval <<-RUBY_EVAL, __FILE__, __LINE__
              def i18n_interpolate(v = {})
                "#{compiled_interpolation_body(string)}"
              end
            RUBY_EVAL
          end

          string
        end