Re: [PATCH] libstdc++: Add test for std::con/disjunction's short circuiting

[Jonathan Wakely <jwakely@redhat.com>]

On Tue, 30 Aug 2022 at 18:14, Patrick Palka via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk?

Yes, thanks for adding this.

>
> libstdc++-v3/ChangeLog:
>
>         * testsuite/20_util/logical_traits/requirements/short_circuit.cc: New test.
> ---
>  .../requirements/short_circuit.cc             | 32 +++++++++++++++++++
>  1 file changed, 32 insertions(+)
>  create mode 100644 libstdc++-v3/testsuite/20_util/logical_traits/requirements/short_circuit.cc
>
> diff --git a/libstdc++-v3/testsuite/20_util/logical_traits/requirements/short_circuit.cc b/libstdc++-v3/testsuite/20_util/logical_traits/requirements/short_circuit.cc
> new file mode 100644
> index 00000000000..b6a8091cdb0
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/logical_traits/requirements/short_circuit.cc
> @@ -0,0 +1,32 @@
> +// { dg-do compile { target c++17 } }
> +
> +#include <type_traits>
> +
> +template<class T> struct A { using type = typename T::type; };
> +using invalid = A<void>;
> +
> +// [meta.logical]/3: For a specialization conjunction<B_1, ..., B_n>, if
> +// there is a template type argument B_i for which bool(B_i::value) is false,
> +// then instantiating conjunction<B_1, ..., B_n>::value does not require the
> +// instantiation of B_j::value for j > i.
> +
> +static_assert(!std::conjunction_v<std::false_type, invalid>);
> +static_assert(!std::conjunction_v<std::false_type, invalid, invalid>);
> +static_assert(!std::conjunction_v<std::false_type>);
> +
> +static_assert(!std::conjunction_v<std::true_type, std::false_type, invalid>);
> +static_assert(!std::conjunction_v<std::true_type, std::false_type, invalid, invalid>);
> +static_assert(!std::conjunction_v<std::true_type, std::false_type>);
> +
> +// [meta.logical]/8: For a specialization disjunction<B_1, ..., B_n>, if
> +// there is a template type argument B_i for which bool(B_i::value) is true,
> +// then instantiating disjunction<B_1, ..., B_n>::value does not require the
> +// instantiation of B_j::value for j > i.
> +
> +static_assert(std::disjunction_v<std::true_type, invalid>);
> +static_assert(std::disjunction_v<std::true_type, invalid, invalid>);
> +static_assert(std::disjunction_v<std::true_type>);
> +
> +static_assert(std::disjunction_v<std::false_type, std::true_type, invalid>);
> +static_assert(std::disjunction_v<std::false_type, std::true_type, invalid, invalid>);
> +static_assert(std::disjunction_v<std::false_type, std::true_type>);
> --
> 2.37.2.490.g6c8e4ee870
>