swapcase()
Returns a copy of str with uppercase alphabetic characters converted to lowercase and lowercase characters converted to uppercase. Note: case conversion is effective only in ASCII region.
"Hello".swapcase #=> "hELLO" "cYbEr_PuNk11".swapcase #=> "CyBeR_pUnK11"
static VALUE rb_str_swapcase(VALUE str) { str = rb_str_dup(str); rb_str_swapcase_bang(str); return str; }