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Subject: Re: [boost] Unittest capability for meta-programs feedback request
From: Ben Robinson (icaretaker_at_[hidden])
Date: 2011-09-28 02:06:57

I have created an example of using the proposed assertion macros, by
incorporating them into Boost Unit, and then creating a unit test which was
previously not possible to write. With the current Boost Unit, the
following unit test can be written:

BOOST_AUTO_TEST_CASE(passing_assignment_compatible_units) {
    BOOST_CHECK_NO_THROW( quantity<length> L = 2.0 * meters; );

And now, after incorporating BOOST_METATEST_MSG into Boost Unit, it is now
possible to write the following unit test:

BOOST_AUTO_TEST_CASE(failing_assignment_incompatible_units) {
    BOOST_CHECK_THROW( quantity<length> L = 2.0 * meters * meters;,
metatest_exception );

The required modification to Boost Unit, was to add the following templated
constructor to boost::units::quantity:

        template <class rhs_type>
        quantity(const rhs_type& source) : val_()

In the unmodified library, the lack of this constructor would produce the
compiler error, when an incorrect assignment requiring this constructor was
made. This makes an interesting point, that I have written additional code
to *explicitly* express the intended failure consequence of invoking this
constructor, instead of relying *implicitly *on the lack of such a

A significant benefit of this change, is that the compiler error message now
produced, is now controlled by the BOOST_MPL_ASSERT_MSG macro, instead of a
generic compiler specific message. I don't think I need to justify
why BOOST_MPL_ASSERT_MSG is preferred to a generic compiler error, with this
group. :))

The source for this example has been uploaded to the Metatest git repository
at, in the example_boost_unit

Thank you all again in advance for your feedback,

Ben Robinson, Ph.D.

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