Question

I am trying to extend the ruby string class like this:

String.class_eval do
  def clear!
    # Here I want the string value to be set to empty string. The following code is not working.
    self = ''
  end
end

Answer 1

Use String#replace:

class String
  def clear!
    replace ""
  end
end

x = "foo"
x.clear!
p x
#=> ""

Similarly available: Array#replace and Hash#replace.

Alternatively, and far less cleanly:

class String
  def clear!
    gsub! /.+/m, ''
  end
end

class String
  def clear!
    slice!(0,-1)
  end
end

# ...and so on; use any mutating method to set the contents to ""