Re: [boost] [Concepts] Definition. Was [GSoC] [Boost.Hana] Formal review request

Subject: Re: [boost] [Concepts] Definition. Was [GSoC] [Boost.Hana] Formal review request
From: Roland Bock (rbock_at_[hidden])
Date: 2014-08-05 07:27:31

On 2014-08-05 12:14, Mostafa wrote:
> On Tue, 05 Aug 2014 01:59:34 -0700, Roland Bock <rbock_at_[hidden]> wrote:
>
>> On 2014-08-05 10:30, Krzysztof Czainski wrote:
>>> 2014-08-05 6:33 GMT+02:00 Michael Shepanski <mps_at_[hidden]>:
>>>
>>>> On 5/08/2014 1:39 AM, Roland Bock wrote:
>>>>
>>>>> On 2014-08-04 13:32, Mostafa wrote:
>>>>>
>>>>>> Concepts are sets of types
>>>>>>
>>>>> I think you are mistaken. A concept is a set of requirements,
>>>>>
>>>> I am under a New Year's resolution not to start philosophical
>>>> arguments,
>>>> but this one has already begun, so ...
>>>>
>>> Please don't forget, that not all requirements can be checked at
>>> compile
>>> time. For example: TotallyOrdered. Just by checking, that an expression
>>> (a<b) is valid and yields something boolable, you can't distinguish
>>> between
>>> TotallyOrdered, PartiallyOrdered, or maybe neiter.
>>>
>>> So, while I think it doesn't matter, whether we view concepts as
>>> sets of
>>> types or requirements
>> Well, if you consider TotallyOrdered a concept, then by this reasoning,
>> it cannot be a set of types. But it could be a set of requirements :-)
>
> Yes it can. TotallyOrdered := { T | if a,b,c are objects of T then ... }

As Kris pointed out: Whether an object is TotallyOrdered or not cannot
be checked at compile time because it does not depend on the type alone,
it also depends on runtime information. Hence, not a set of types.

Best,

Roland