Re: [boost] Review: concept checks.

From: Jeremy Siek (jsiek_at_[hidden])
Date: 2000-11-25 12:11:24

Hi John,

Well, if we really want to minimize the requirements for lower_bound
(which I agree in general is a very good idea) then we have to define
strict weak ordering in a much different way, or not require strict weak
ordering for lower_bound() and require something else.

The definition of strict weak ordering in 25.3 makes lots of uses of T < T
and value_type < value_type.

So does anyone know how to either:

1) create an alternate definition of strict weak ordering
 that only uses value_type < T.

or

2) create some alternate requirement (not strict weak ordering)
  that is enough to ensure lower_bound() will work.

I'm no expert on sorting, so I don't know if 1) or 2) is possible,
or what form they would take.

-Jeremy

On Sat, 25 Nov 2000, John E. Potter wrote:
> We are talking about lower_bound?  The only requirement to write the
> algorithm is iterator_traits<ForwardIterator>::value_type < T.  Since
> there is only one object of type T available to the algorithm, it is
> nonsense to require T to be less than comparable.  Conversions are
> evil and requiring one is bad.  It is much more likely that value_type
> could be converted to T anyway.
> 
> > if someone wants to add extra
> > signatures to the comparison operator to avoid unnecessary coversions then
> > that's OK, but I don't see LessThanComparable2<A,B> as being required here
> > (although it can't do any harm).
> 
> Requiring anything that is not required does much harm.  It makes the
> library harder to use for no reason.  It is possible to write lower_bound
> using T < value_type and value_type < value_type and maybe even T < T,
> but the streight forward algorithm uses none of them and is optimal.
> 
> Please stop trying to check concepts that do not exist.  If the
> standard has a meaningless requirement, fix the standard, do not break
> the library.
> 
> John
> 
> 
> 
> 
> 

----------------------------------------------------------------------
 Jeremy Siek                        www: http://www.lsc.nd.edu/~jsiek/
 Ph.D. Candidate                  email: jsiek_at_[hidden]
 Univ. of Notre Dame         work phone: [phone]
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