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From: Howard Hinnant (hinnant_at_[hidden])
Date: 2002-03-20 15:57:50

Agreed is_copyable<T> would be very nice. What Rani's has_key_type
might give us is a way to put a version number into an existing class
interface. One could check for a version_number type in a class, and if
it isn't there, call it version 1. If it is there, then the version
number is T::version. Given the class's version number, and its
documentation, you can make assumptions on the class interface.

This might be a way to add to the interface of something like allocators
without breaking everybody's existing allocators. Containers could
check the allocator's version number and then instantiate the
appropriate code.


On Wednesday, March 20, 2002, at 12:44 PM, David Abrahams wrote:

> I did some more thinking about that this morning, including reading the
> relevant part of the standard. It seems to me that we're still missing
> some very important predicates which we could get from a legality
> checker, like is_copyable<T>.
> -Dave
> ----- Original Message -----
> From: "Howard Hinnant" <hinnant_at_[hidden]>
> To: <boost_at_[hidden]>
> Sent: Wednesday, March 20, 2002 9:17 AM
> Subject: Re: [boost] is_class
>> On Wednesday, March 20, 2002, at 01:57 AM, David Abrahams wrote:
>>> I wonder if this gives Howard his general "tell me if this
>>> construct compiles or not" compile-time check?
>> I believe it goes a long way towards it. This is extraordinary code.
>> I'm still trying to sort out the ramifications...
>> -Howard
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