@Override
    public FastStr replaceFirst(String regex, String replacement) {
        return unsafeOf(Pattern.compile(regex).matcher(this).replaceFirst(replacement));
    }
@ Override public FastStr replaceFirst ( String regex , String replacement ) { return unsafeOf ( Pattern . compile ( regex ) . matcher ( this ) . replaceFirst ( replacement ) ) ; }
Wrapper of {@link String#replaceFirst(String, String)} but return FastStr inance

@param regex the regular expression specifies the place to be replaced
@param replacement the string to replace the found part
@return a FastStr that has the first found part replaced