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

Subject: Re: [boost] [Review:Algorithms] Order of args to clamp
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2011-09-25 18:55:55

AMDG

On 09/25/2011 03:26 PM, Jeffrey Lee Hellrung, Jr. wrote:
> On Sun, Sep 25, 2011 at 3:15 PM, Steven Watanabe <watanabesj_at_[hidden]>wrote:
> 
>> Precondition:  operator< defines an ordering on objects of type U.   For
>> any
>>> 2 objects a and b of types A and B, respectively, where A and B are each
>> one
>>> of {T,L,H}, a < b is equivalent to (U)a < (U)b.  !(hi < lo).
>>
>> This should be !(U(hi) < U(lo)).
>>
> 
> Equivalent, given the preconditions, no?
> 
> Your restrictions on the comparison are
>> too strict.  You don't want to constrain
>> (lo < lo), (hi < hi), (hi < lo), or (lo < hi),
>> because that would exclude T = std::string,
>> L = H = const char*.
>>
> 
> I don't follow.
> - (lo < lo) and (hi < hi) should both return false, so that clamp(x, x, hi)
> and clamp(x, lo, x) both return x.  I think this is desirable.

Sorry.  I was actually thinking in terms of the types,
rather than the actual values.

> - I think !(hi < lo) is a reasonable precondition so that the result is
> independent of whether you first compare to lo or hi.

I agree, the only question is how to express it.

> How do these preconditions exclude T == std::string and L == H == char const
> *?  Doesn't the STL define comparison operators between these types that do
> the "obvious" thing?
> 

Comparing const char*'s compares the pointers,
not the contents.

In Christ,
Steven Watanabe