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

You are trying to say something that makes no sense. You are asking the compiler to guess T from your arguments, but then you do not provide any argument.

The following code does compile, and does what you want:

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

template void foo() {
  foo([]() {}); // Call actual implementation with empty lambda
}

void bar() {
  foo([&](){ /* implementation here */ }); // this compiles
  foo(); // this now compiles as well
}