First of all, let's try to make your code a little simpler:
// No need to create a circle unless it is clearly necessary to
// demonstrate the problem
// Your Rect2f defines a default constructor, so let's use it for simplicity.
shared_ptr<Shape> rect(new Rect2f());
Okay, so now we see that the parentheses are clearly balanced. What else could it be? Let's check the following code snippet's error:
int main() {
delete new T();
}
This may seem like weird usage, and it is, but I really hate memory leaks. However, the output does seem useful:
In function 'int main()':
Line 2: error: expected type-specifier before 'T'
Aha! Now we're just left with the error about the parentheses. I can't find what causes that; however, I think you are forgetting to include the file that defines Rect2f.