🚀 go-pugleaf

In article 779@aztec.co.za, dharley@aztec.co.za (David Harley) writes:
>
>Steve Clamage (clamage@Eng.Sun.COM) wrote:
>
>: A using-directive will solve your problem without generating any extra code.
>
>: class B1 { public: int foo(int); };
>: class B2 { public: int foo(char); };
>: class D : public B1, public B2 {
>: public:
>: 	using B1::foo; // "using" applies to a name, not to a signature
>: 	using B2::foo;
>: 	double foo(double); // new overload
>: };
>
>[ snip ]
>
>I have never understood why an overloaded member of a subclass hides a
>superclass's member. It seems to be illogical and contradicts the
>behaviour of non-class members. (It is also very irritating.)

The fundamental rule of scopes is that a name declared in a scope hides
all instances of that name in all outer scopes. Therefore, overloading
cannot occur across scopes. Base class scope is a different scope from
derived class scope, and encloses the derived class scope.

If overloading could occur across scopes, you would need a lot of special
rules. Example:

	class A { ... int f(int); };
	class B : public A { ... char* f; };
	class C : public B { ... double f(double); };

	A a;
	B b;
	C c;

	a.f(1)	 // OK, call A::f(int)
	b.f[0]	 // OK, access B::f
	b.f(1)	 // If OK, why? If not, why not?
	c.f(1.0) // OK, call C::f(double)
	c.f[0]	 // If OK, why? If not, why not?
	c.f(1)	 // call C::f(double) or A::f(int), and why?

This simple example would require special-case rules if we don't keep the
existing fundamental rule of scopes.

>What is 'using'? It does not seem to be standard.

It was added to the C++ draft standard 2 or 3 years ago. You can read about
it in the discussion of namespaces in "The Design and Evolution of C++" or
in the public-review copy of the draft standard which was posted on
several public FTP sites last May.

---
Steve Clamage, stephen.clamage@eng.sun.com



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