BOOST_TEST( ..., per_element() ) erroneously requires collections are comparable

[Tony Lewis <tonyelewis@…>]

Thanks for the new BOOST_TEST() and per_element() tools, which look very useful.

Unfortunately, I'm having trouble with comparing collections that aren't themselves comparable but have comparable elements.

As I understand the requirements documentation for the BOOST_TEST / per_element() tools, they should only require that the two collections' elements are comparable, not necessarily the two collections themselves. I think this approach makes a lot of sense.

However, when I try to compile the following under either g++ -std=c++11 or clang -std=c++11 -stdlib=libc++, the compilers complain that collections aren't comparable :

#define BOOST_TEST_MODULE comp_by_elem_mod

#include <boost/test/included/unit_test.hpp>

#include <iterator>
#include <vector>

struct my_class final {
        std::vector<int> the_ints = { 1, 2, 3 };

        using const_iterator = std::vector<int>::const_iterator;

        const_iterator begin() const {
                return std::begin( the_ints );
        }
        const_iterator end() const {
                return std::end( the_ints );
        }
};

BOOST_AUTO_TEST_CASE( comp_by_elem ) {
        const my_class         a{};
        const std::vector<int> b = { 1, 2, 3 };
        BOOST_TEST( a == b, ::boost::test_tools::per_element() );
}

I'll attach compiler errors.

Many thanks.

[Tony Lewis <tonyelewis@…>]

clang

[Tony Lewis <tonyelewis@…>]

g++ compilation errors

[Raffi Enficiaud]

Fixed in develop, assigning to keep track.

[Raffi Enficiaud]

merged to master

[Tony Lewis <tonyelewis@…>]

I'm still seeing this problem in Boost 1.60.0. Is that expected?

[Raffi Enficiaud]

Hi,

I just tried your example, and I can reproduce the problem. This is because your class my_class_final does not follow the requirements for the sequence as defined here.

After adding members size and value_type it works as expected. Would you please confirm?

[Tony Lewis <tonyelewis@…>]

Thanks for this, yes I can confirm that I'm able to fix my problems by adding size and value_type. Sorry - I should have RTFM properly :-).

To make it harder for others to repeat my mistake, it might be useful to:

• add a note here to explicitly state that the comparators must meet the requirements of a sequence and then link to the definition further down that page that you highlighted.
• ideally use a Sequence concept to make the compiler errors more helpful. I realise that you may be keen to avoid adding a dependency to the Boost Concept library.

Again, thanks and apologies. I'm happy for you to close this ticket.

[Raffi Enficiaud]

I added an entry to the doc as you suggested (rev 1976cc2). We are not too keen in adding dependencies though.

Thanks, Raffi

[Tony Lewis <tonyelewis@…>]

Great, thanks.