id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
13202,adjacent_filtered postcondition docs differ from behaviour,Tony Lewis <tonyelewis@…>,Neil Groves,"I think the documentation for `adjacent_filtered`'s postcondition, ie:

> For all adjacent elements `[x,y]` in the returned range, `bi_pred(x,y)` is `true`.

…isn't quite right. For example, this:

{{{
#!cpp
#include <boost/range/adaptor/adjacent_filtered.hpp>

#include <iostream>
#include <vector>

int main() {
	const std::vector<int> a = { 0, 1, 2, 3, 4, 5, 6 };

	const auto b = a | boost::adaptors::adjacent_filtered(
		[] (const int &x, const int &y) {
			return ( y % 2 == 1 ) && ( y == x + 1 );
		}
	);
	for (const auto &x : b) {
		std::cerr << x << ""\n"";
	}
}
}}}

…outputs:

{{{
0
1
3
5
}}}

Yet two of the pairs of adjacent elements `[x,y]` in this range fail `bi_pred(x,y)` (because they differ by 2, not 1).

I think it's more like: `bi_pred` is true on each element in the returned range preceded by the element that preceded it in the //original// range (not in the //returned// range).",Bugs,new,To Be Determined,range,Boost Development Trunk,Optimization,,"range,adjacent_filtered,documentation,postcondition,predicate,adaptor",