Re: [boost] [Review:Algorithms] Order of args to clamp

Subject: Re: [boost] [Review:Algorithms] Order of args to clamp
From: Marshall Clow (mclow.lists_at_[hidden])
Date: 2011-09-23 19:04:56

On Sep 23, 2011, at 12:01 PM, Jeffrey Lee Hellrung, Jr. wrote:

> On Fri, Sep 23, 2011 at 9:34 AM, Marshall Clow <mclow.lists_at_[hidden]>wrote:
> 
>> 
>> On Sep 23, 2011, at 9:21 AM, Phil Endecott wrote:
>> 
>>> Dear All,
>>> 
>>> Some quick comments about the proposed clamp() function:
>> 
> [...]
> 
>>> Like min & max, clamp has a single type template parameter; what are the
>> implications of this?  For example, if I pass a mixture of std::string and
>> const char* arguments, what will happen? Ideally, (a) all combinations would
>> compile, and (b) conversions from const char* to std::string will only
>> happen when necessary, not unconditionally for all of the arguments.  (Maybe
>> that is asking too much, though.)
>> 
>> Dunno; I'll put it on the list of things to think about.
>> 
> Isn't this *precisely* why we have common_type now? :)
> 
> I haven't actually looked at the documentation, but I'm gathering that
> std::less<T> is the default comparison function object, in which case I
> would suggest this should be replaced with some other function object with a
> templated operator() that wraps operator<; this should avoid unnecessary
> temporaries in more cases.

Are you talking about something like this? (typed w/o benefit of compiler)

namespace boost { struct less
{
    typedef bool result_type;

    template <typename T> // T models Regular
    bool operator()(const T& x, const T& y) const { return std::less<T>()(x, y); }

    template <typename T, typename U>
    bool operator ()(const T& x, const U&y) const { return std::less<boost::common_type<T, U>() ( x, y )); }
};
}

-- Marshall

Marshall Clow     Idio Software   <mailto:mclow.lists_at_[hidden]>

A.D. 1517: Martin Luther nails his 95 Theses to the church door and is promptly moderated down to (-1, Flamebait).
        -- Yu Suzuki