Re: [Boost-users] Library Interface Design

18 Sep 2006


      "Matthias Hofmann"  writes:
...
"David Abrahams"  schrieb im Newsbeitrag 
news:87bqphhxjl.fsf@pereiro.luannocracy.com...
...
David Walthall  writes:
...
The only time I have found it useful to have default-constructed objects
that are otherwise unusable is when I need to store them in a map or
other container that requires a default constructible object.
No standard containers have that requirement, though.
This seems to be another defect, as the standard also defines the following 
constructor:
explicit vector(size_type n, const T& value = T(),
const Allocator& = Allocator());
Now how is the following code supposed to compile:
#include <vector>
struct X
{
    X( int ) {}
};
void f()
{
    // Error: No default constructor for X.
    std::vector<X> v( 5 );
}
That's not a defect; it's simply _not_ supposed to compile!

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com