Re: [boost] [type_traits] adding is_less_comparable<T>, etc.

Subject: Re: [boost] [type_traits] adding is_less_comparable<T>, etc.
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-08-31 13:32:09

[subject adjusted a bit]

Frédéric Bron wrote:
>
> Anybody wanting to review this very short addition to type_traits?

remove_cv.html is not in the archive (the link from index.html was broken).

The links for the additions are not in alphabetical order on index.html.

Even if you didn't invent the code, you assembled and documented it, so your name should be in the copyright notice (in the documentation), right?  Add others to the list as you think appropriate.

Your HTML formatting differs from the original, though that could be the means by which it was generated rather than a difference in the formatting of your files.

Your content will appear in a single page, reference.html, if added to Boost.TypeTraits, so why create separate pages now?

The description of is_greater_comparable should be more specific:

   If a value of type T can be compared with another using
   operator > to determine whether the first is greater than
   the other, then inherits from true_type, otherwise
   inherits from false_type.

That rewrite anticipates the question you asked, below.

I think is_greater_than can be less restrictive than it is.  std::greater() provides an operator that permits comparing unrelated types as T's.  Therefore, I wonder if this would work:

   template <class T, class U = T>
   struct is_greater_comparable;

Then, is_greater_comparable<int, float> would inherit from true_type.

Similar changes would apply to the other comparison types.

> I can add that one important question of the review is: should we
> report that T is less comparable if T<T returns void?

I think that is not appropriate as the whole point of less-than-comparable is to be able to determine whether one instance is less than another, not that "operator <" is supported.

The same applies to the other comparison operators.

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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