String& String::operator$=($const String& other$)\{$ if $($this $!=$ &other$)\{$ delete$[]$ buffer; len $=$ other.len; if $($len $>0)\{$ buffer $=$ new char$[$len$]$; for $($int i $=0$; i $<$ len; i$++)\{$ buffer$[$i$]=$ other.buffer$[$i$]$; $\}\}$ else $\{$ buffer $=$ nullptr; $\}\}\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_//$line$($s$)$ of code go$($es$)$ here $\}$