/*
 *  call-seq:
 *     str.sub(pattern, replacement)         => new_str
 *     str.sub(pattern) {|match| block }     => new_str
 *  
 *  Returns a copy of <i>str</i> with the <em>first</em> occurrence of
 *  <i>pattern</i> replaced with either <i>replacement</i> or the value of the
 *  block. The <i>pattern</i> will typically be a <code>Regexp</code>; if it is
 *  a <code>String</code> then no regular expression metacharacters will be
 *  interpreted (that is <code>/\d/</code> will match a digit, but
 *  <code>'\d'</code> will match a backslash followed by a 'd').
 *     
 *  If the method call specifies <i>replacement</i>, special variables such as
 *  <code>$&</code> will not be useful, as substitution into the string occurs
 *  before the pattern match starts. However, the sequences <code>\1</code>,
 *  <code>\2</code>, etc., may be used.
 *     
 *  In the block form, the current match string is passed in as a parameter, and
 *  variables such as <code>$1</code>, <code>$2</code>, <code>$`</code>,
 *  <code>$&</code>, and <code>$'</code> will be set appropriately. The value
 *  returned by the block will be substituted for the match on each call.
 *     
 *  The result inherits any tainting in the original string or any supplied
 *  replacement string.
 *     
 *     "hello".sub(/[aeiou]/, '*')               #=> "h*llo"
 *     "hello".sub(/([aeiou])/, '<\1>')          #=> "h<e>llo"
 *     "hello".sub(/./) {|s| s[0].to_s + ' ' }   #=> "104 ello"
 */

static VALUE
rb_str_sub(argc, argv, str)
    int argc;
    VALUE *argv;
    VALUE str;
{
    str = rb_str_dup(str);
    rb_str_sub_bang(argc, argv, str);
    return str;
}