[boost] Re: Re: singleton template template parameters

From: Jonathan Turkanis (technews_at_[hidden])
Date: 2005-02-16 18:58:05

Jason Hise wrote:
> Jonathan Turkanis wrote:
>
>> I suggested you follow policy_ptr and use mpl metafunction classes
>> as policy template parameters. See, for instance, the array storage
>> policy: http://tinyurl.com/6tbhu.
>>
>> It looks like this:
>>
>>    template <typename T>
>>    class array_storage_
>>    { ... };
>>
>>    struct array_storage
>>    {
>>        typedef storage_policy_tag policy_category;
>>
>>        template <typename T>
>>        struct apply
>>        {
>>            typedef array_storage_<T> type;
>>        };
>>    };
>>
>> Jonathan
>>
> is this essentially the equivalent of the standard allocator's rebind?

The difference is that an allocator is designed *both* to be used by itself and
to generate other allocator types. A metafunction class is generally just a type
generator. (In the above example there is also some auxilliary machinery to
support identifying template arguments by category rather than position.)

Jonathan