c++ - default value of const reference parameter -

currently have 2 functions:

void foo(const & a) {   ...   result = ...   result += handle(a); // 1   bar(result); }  void foo() {   ...   result = ...   bar(result); } 

all code in foo() same except 1.

can merge them 1 function following?

void foo(const & = 0) {   ...   ...   if (a) result += handle(a); // won't work, can similar?   bar(result); } 

btw, parameter has reference keep interface unchanged.

you can use null object pattern.

namespace {   const null_a; // (possibly "extern") }  void foo(const & = null_a) {   ...   result = ...   if (&a != &null_a) result += handle(a);   bar(result); }