Re: [boost] RFC: Sequence Properties and Boost Algorithm/Functional

Subject: Re: [boost] RFC: Sequence Properties and Boost Algorithm/Functional
From: Marshall Clow (mclow.lists_at_[hidden])
Date: 2010-01-22 18:29:00

On Jan 22, 2010, at 3:24 PM, Marshall Clow wrote:

> 
> On Jan 22, 2010, at 2:02 PM, Grant Erickson wrote:
> 
>> For a recent project, I needed to inquire about a sequence of objects and
>> make a determination as to whether the sequences were:
>> 
>>   * Increasing
>>   * Strictly Increasing
>>   * Decreasing
>>   * Strictly Decreasing
>> 
>> Looking through STL, Boost documentation, Boost sources and headers and the
>> Boost mailing lists I was able to find neither an existing algorithm or
>> stateful unary predicate functor for accomplishing this for a pair of input
>> iterators. However, I was a bit surprised considering that this seems like a
>> sequence property query that would tend to come up fairly often and serve a
>> general utility. Did I just fail to form the proper search/query or am I
>> overestimating the general utility?
> 
> I've got this floating around from a while back (as well as the other three - increasing, decreasing, and strictly_decreasing ).
> Maybe these should go in the algorithms library:
> 
> template<typename T>
> bool is_strictly_increasing ( T* begin, T* end ) {
> //	Empty sequences are strictly increasing
> 	if ( begin == end )
> 		return true;
> 
> 	T* iter = begin;
> 	T  val  = *iter++;
> 	
> 	while ( iter != end ) {
> 		if ( ! ( *iter > val ))
> 			return false;
> 		val = *iter++;
> 		}
> 	return true;
> 	}

Funny that.

Three minutes after posting my code, I noticed that I worked all the comparisons to use ">" (and the code *does* work),
rather than using "<" (or std::less), which is what I meant to do when I wrote this code.

Nothing like showing your work to a large audience to find problems.

-- Marshall