Re: Template default constructor possible?
* Ian Collins:
I've never had cause to try this before, but is it possible to have a
template default constructor?
I wish to pass the type of a singleton to a class and use the static
methods of that singleton object in the class, for example:
template <typename Item>
bool getItemValue() {
return Item::getValue();
}
struct Item { static bool getValue(); };
struct X
{
typedef bool (*GetFn)();
const GetFn getFn;
template <typename T> X( const T& )
: getFn( getItemValue<T> ) {}
};
works, but requires a public default constructor for T.
There's no way to call a templated constructor with no arguments. So
you can have that templated constructor, but not use it. However, it's
no big deal create an argument type that can carry a type for you, e.g.
template< typename T > struct UseMethodsOf {};
template< typename T >
UseMethodsOf<T> useMethodsOf(){ return UseMethodsOf<T>(); }
struct X
{
...
template< typename T >
X( UseMethodsOf<T> ): getFn( &getItemValue<T> ) {}
};
...
X foo( useMethodsOf<Whatever>() );
Cheers, & hth.,
- Alf
--
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?