Re: Non-virtual destructors & valarray memory allocation
* Earl Purple -> Alf P. Steinbach:
Sometimes the point of deriving from a class is only to extend.
At least one popular language even uses the keyword "extends" to
designate class derivation.
That popular language also has every class deriving from an Object
class, and doesn't have destructors at all, so no need to worry about
virtual ones. Nor does it support free-functions although you can
create a class simply to provide functions. It does have a "final"
keyword though.
Now you're really bad-mouthing Eiffel...
[snip]
constructors: Easy. Suppose I want to be able to create a vector from a
static array. Let's create a function make_vector.
template < typename T, size_t N >
std::vector< T > make_vector( const T (&arr)[N] )
{
return std::vector( arr, arr+N );
}
std::vector< int > = make_vector( { 1, 2, 3, 4, 5 } );
(I think that should compile anyway)
There are some differences regarding both efficiency and functionality.
[snip]
Some standard library classes have protected members.
Some standard library classes are meant to be derived from like
basic_streambuf. Are there any that have protected members and no
virtual methods and no virtual destructor?
std::binder1st (?20.3.6.1)
std::binder2nd (?20.3.6.3)
std::queue (?23.2.3.1)
std::priority_queue (?23.2.3.2)
std::stack (?23.2.3.3)
std::map (?23.3.1/2)
std::multimap (?23.3.2/2)
std::reverse_iterator (?24.4.1.1)
std::back_insert_iterator (?24.4.2.1)
std::front_insert_iterator (?24.4.2.3)
std::insert_iterator (?24.4.2.5)
std::ios_base (?27.4.2)
std::basic_ios (?27.4.4)
And maybe more.
[snip]
Is there a standard policy with regards to the behaviour of
tr1::shared_ptr deleters? If so, what is it?
Not sure, but a deleter is rather useless if it isn't propagated when
the smart-pointer is copied.
Summing up, when deriving from a standard library class would be in
order except for the lack of virtual destructor, just derive, but don't
destroy polymorphically -- use smart pointers if that's an issue.
Yes obviously. But it is probably still wrong to derive from concrete
classes most of the time.
Well, I see no technical reason.
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
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