Consider the following code in C$++$:

class string$\_$map $\{$

string cached$\_$key;

string cached$\_$val;

const string complex$\_$lookup$($const string key$)$;

$//$ body specified elsewhere public:

const string operator$[]($const string key$)\{$ if $($key $==$ cached$\_$key$)$ return cached$\_$val; string rtn$\_$val $=$ complex$\_$lookup$($key$)$; cached$\_$key $=$ key;

cached$\_$val $=$ rtn$\_$val;

return rtn$\_$val;

$\}$

$\}$;

Suppose that string$\_$map::operator$[]$ contains the only call to complex$\_$ lookup anywhere in the program. Explain why it would be unwise for the programmer to expand that call textually in$-$line and eliminate the separate function.