Default lambda as templated parameter of a function

Question

Consider the following code

template void foo(const T& t = []() {}) {
  // implementation here
}

void bar() {
  foo([&         


        

Answer 1

Consider overloading it directly:

template 
void foo(void) {
  foo([](){});
}

See CppReference:

Non-deduced contexts

4) A template parameter used in the parameter type of a function parameter that has a default argument that is being used in the call for which argument deduction is being done:

Type template parameter cannot be deduced from the type of a function default argument: template void f(T = 5, T = 7);

void g()
{
    f(1);     // OK: calls f(1, 7)
    f();      // error: cannot deduce T
    f(); // OK: calls f(5, 7)
}