Description Kamil Mierzejewski 2021-07-30 07:55:21 EDT

The parser is unable to properly resolve function call, to a function which takes a function pointer as argument, with a lambda expression as argument when, the lambda has argument of auto type and its return type depends on argument type:


struct Obj {
	bool bmem;
};

class ObjPtr
{
public:
	const Obj* operator->() const { return &m_data; }
    Obj m_data;
};


Obj* func(bool(*predicate)(const ObjPtr&)  = {})
{
	return 0;
}

int main() {
    return func([](const auto& arg)
            {
                return arg->bmem;
            });

The call to "func" in main gets underlined as 'Invalid argument'. It only happens if the "func" argument type has overloaded operator-> and the result type of lambda is inferred from a "->" dereference of argument.

If I use ObjPtr instead of auto, it works correctly:

int main() {
    return func([](const ObjPtr& arg)
            {
                return arg->bmem;
            });
}