E. Gladyshev
Guest
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 Posted: Fri Feb 27, 2004 2:35 pm Post subject: Policies in templates with "variable" number of parameters. |
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What is the best way to add a policy to a template like tuple<>?
The most obvious option that I can see is:
//all tuple assignment policies must be derived from this class.
struct tuple_assignment_policy {};
template < typename T1 = empty, typename T2 = empty, ... >
struct tuple
{
struct default_tuple_assignment_policy : tuple_assignment_policy {...};
typedef typelist<T1, T2, ...> types;
//find_derived< TypeList, Type, DefaultType >
//searches the TypeList for a type that is derived from Type
//if no such type is found, DefaultType is returned
typedef
typename find_derived< types,
tuple_assignment_policy,
default_tuple_assignment_policy >::type assignment_policy;
//use assignement_policy
...
};
struct my_assignment_policy : tuple_assignment_policy {...};
tuple< int, double > t1; //uses default_tuple_assignment_policy
tuple< int, double, char, my_assignment_policy > t2; //uses
my_assignment_policy
Eugene
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