Re: Isn't this a polymorphic call?

From:

James Kanze <james.kanze@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 29 May 2008 00:54:55 -0700 (PDT)

Message-ID:

<425f74c2-8942-4f37-8413-71e9c2b506af@l64g2000hse.googlegroups.com>

On May 29, 2:15 am, "A. Bolmarcich" <agge...@earl-grey.cloud9.net>
wrote:

On 2008-05-28, Arindam <arindam.muker...@gmail.com> wrote:

On May 29, 2:14 am, Victor Bazarov <v.Abaza...@comAcast.net> wrote:

Arindam wrote:

#include <cstdio>

struct Test {
void bar() {
foo();
}
private:
virtual void foo() {
printf("Test\n");
}
};

struct Test2 : public Test {
void foo() {
printf("Test2\n");
}
};

int main(int argc, char* argv[])
{
Test2 v;
v.bar();
}

Does the call to v.bar() amount to a polymorphic
invocation of foo()?

Have you tried it? If you have, what happened? If not, why not?

Yes - it prints Test2. So this should be polymorphic right?

It is not polymorphic according to the inventor of C++, who
wrote in "The C++ Programming Language (Third Edition)":

"To get polymorphic behavior in C++, the member functions called must
be virtual and objects must be manipulated through pointers or
references. When manipulating an object directly (rather than through
a pointer or reference), its exact type is known by the compiler so
that run-time polymorphism is not needed."

And? He's calling foo() through a pointer (this), and the call
is resolved polymorphicly.

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