Re: One more foolishness of the C++ Standard
Vladimir Grigoriev wrote:
"Ulrich Eckhardt" <eckhardt@satorlaser.com> wrote in message
news:v63o27-ijd.ln1@satorlaser.homedns.org...
Vladimir Grigoriev wrote:
For example you can define a Point class derived from std::pair. And
your Point class may have arithmetic operators. You may to add a
std::pair object to a Point object but your may not add a Point object
to a std:pair
object.
Why not? If a+b computes then b+a should, too.
Well, when try to build two template classes one derived from another such
a way that the base class will not get a new feature of the derived class.
For example
template <typename T>
class A
{
...
template <typename U>
A( const A<U> & );
...
};
template <typename T>
class B: public A<T>
{
...
template <typename U>
B( const B<U> & );
...
};
and class A for example has no a sum operation while class B has.
So the following should be valid
A a;
B b;
b + b;
b + a;
a + b;
So, a+b computes just as well as b+a, just as I said it should.
however
a + a is not valid
I never claimed it should.
Uli
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