Foo f = Foo(); // no matching function for call to 'Foo::Foo(Foo)' … huh?

Question

class Foo
{
public:
    explicit Foo() {}
    explicit Foo(Foo&) {}
};

Foo d = Foo();

error: no matching function for call to \

Answer 1

You don't want to mark either of those constructors as explicit - the compiler needs to use both of them, particularly the copy constructor, implicitly. What are you trying to achieve by marking them explicit?