Randy said:Since these operators can't be member functions, and since
friend functions can't be declared virtual, how do I make my
inserters and extractors polymorphic?
Since these operators can't be member functions, and since
friend functions can't be declared virtual, how do I make my
inserters and extractors polymorphic?
int main(int argc, char* argv[])
{
Base* b;
b = new Derived;
cout << b;
return 0;
}
Really? So if I did that and I had
class Base
{
...
friend ostream& operator<< (ostream& os, const Base& base);
}
and
class Derived : public Base
{
...
friend ostream& operator<< (ostream& os, const Base& base);
}
and then
int main(int argc, char* argv[])
{
Base* b;
b = new Derived;
cout << b;
return 0;
}
the Derived inserter would be used and not the Base inserter?
friend ostream& operator<< (ostream& os, const Derived& derived);
}
and then
int main(int argc, char* argv[])
{
Base* b;
b = new Derived;
No need to 'new' anything. C++ objects can exist on the stack.
cout << b;
return 0;
}
the Derived inserter would be used and not the Base inserter?
It's just function overloading (like in Java or C#).
[...]
int main(int argc, char* argv[])
{
Base* b;
b = new Derived;
No need to 'new' anything. C++ objects can exist on the stack.
Randy Yates said:Really? So if I did that and I had
class Base
{
...
friend ostream& operator<< (ostream& os, const Base& base);
}
and
class Derived : public Base
{
...
friend ostream& operator<< (ostream& os, const Base& base);
friend ostream& operator<< (ostream& os, const Derived& derived);
Right.
}
and then
int main(int argc, char* argv[])
{
Base* b;
b = new Derived;
No need to 'new' anything. C++ objects can exist on the stack.
cout << b;
return 0;
}
the Derived inserter would be used and not the Base inserter?
It's just function overloading (like in Java or C#).
I'm confused - how can it "just be function overloading?"
This is a run-time selection, not compile-time, right?
I thought the usual usage of the term "function overloading"
was reserved for compile-time overloading, while "polymorphism"
was used for run-time overloading. Am I mistaken?
There is run time and compile time polymorphism AFAIK.
The function call is resolved at compile time. I guess Victor Bazarov
has the right answer how to make inserter/extractor "run-time
polymorphic". Sorry for causing confusion.
Randy said:Victor et al.,
Why are you using the "const" qualifier in
ostream& operator << (ostream& os, Base const& b) {
? And also, is the placement of the reference operator "&"
after "const" required or can it also be after Base, e.g.,
ostream& operator << (ostream& os, Base& const b) {
Let me guess: The first way tells the object pointed to
is constant, the second tells the pointer is constant. ??
Randy said:Victor et al.,
Why are you using the "const" qualifier in
ostream& operator << (ostream& os, Base const& b) {
?
> And also, is the placement of the reference operator "&"
after "const" required or can it also be after Base, e.g.,
ostream& operator << (ostream& os, Base& const b) {
Let me guess: The first way tells the object pointed to
is constant, the second tells the pointer is constant. ??
Randy said:Bullshit.
> What do you think a reference is? It is a pointer
in which the compiler automatically handles
dereferencing. From Schildt's "Teach Yourself C++"
2e, in reference to the function "void f(int &n)",
...each time n is used within f(), it is automatically
treated as a POINTER to the argument used to
call f().
I'm sure that is exactly what a implementation does
with references. Anything else (e.g., copying to a
temporary and then recopying when done) would be
insanely inefficient and pointless.
Pointer isn't a dirty word - don't be afraid to use it.
Randy said:Bullshit. What do you think a reference is? It is a pointer
in which the compiler automatically handles
dereferencing.
> From Schildt's "Teach Yourself C++"
2e, in reference to the function "void f(int &n)",
...each time n is used within f(), it is automatically
treated as a POINTER to the argument used to
call f().
I'm sure that is exactly what a implementation does
with references.
> Anything else (e.g., copying to a
temporary and then recopying when done) would be
insanely inefficient and pointless.
Pointer isn't a dirty word - don't be afraid to use it.
Bullshit. What do you think a reference is? It is a pointer
in which the compiler automatically handles
dereferencing. From Schildt's "Teach Yourself C++"
2e, in reference to the function "void f(int &n)",
...each time n is used within f(), it is automatically
treated as a POINTER to the argument used to
call f().
I'm sure that is exactly what a implementation does
with references. Anything else (e.g., copying to a
temporary and then recopying when done) would be
insanely inefficient and pointless.
Pointer isn't a dirty word - don't be afraid to use it.
--Randy Yates
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