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From: "Paul Mensonides" <pmenso57@home.com>
Newsgroups: comp.std.c++
Subject: Re: All I want for Christmas (was C++0x)
Date: Fri, 18 May 2001 07:44:51 GMT
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Xref: archiver1.sj.google.com comp.std.c++:4940

Hey, Andrei, what do you think of some type of templated parameter list?  For
example...

template<class T> class SomeCollection {
    private:
        unsigned m_size;
        T* m_v;
    public:
        template<class U, V(...)> void for_each(U (T::* pm)(V), V) {
            for (int i = 0; i < m_size; ++i) {
                m_v[i].*pm(#V); // #V indicates values rather than type
            }
        }
};

Which, for a given call:

class MyClass {
    public:
        void get(int, int);
};

void f() {
    SomeCollection<MyClass> x;
    //populate x...
    x.for_each(&MyClass:get, 0, 0); // possible disambiguation of &MyClass::get,
maybe: &MyClass::get(int, int) ?
}

where for_each expands to: // allowing type "void" to be used as a return type

    void SomeCollection<MyClass>::for_each(void (MyClass::* pm)(int, int), int
unnamed_1, int unnamed_2) {
        for (int i = 0; i < m_size; ++i) {
            m_v[i].*pm(unnamed_1, unnamed_2);
        }
    }

My example may be going for the most-convoluted award, but the idea anyway could
be a good one.  Transparent use of templated parameter lists.  I think this
would make some types of generic programming significantly easier.  (I'll delay
a further tirade about the semantics of overloading operator->*() for
pointer-to-member-function types and how annoying that is.)

What do you think?
Thanks for the book, by the way.  It was an eye-opener! :)
(Unfortunately, all that I have to use right now is VC++ :( , so most of it
won't compile.)

Paul Mensonides

| By the way, if I had my way, I'd have "if" on compile-time constants not
| compile the branch that's guaranteed not to execute. Kind of like template
| functions that are not instantiated unless used. That would simplify a lot
| of generic code - now I have to use Int2Type all the time.

Agreed, that is annoying in one-or-the-other-but-not-both situations...

template<class X, bool T> void f() {
    X* x = 0;
    if (T) {
        x = new X(0);
    }
    else {
        x = new X;
    }
}

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