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Experiment with constexpr traits in enable_if.

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So the `constexpr` traits do not really look better here.  But
they may be better for writing linear code in complex trait
processing, as opposed to complicated recursive code.  Still
to be determined.  However, If I stay with this and if
`std::find_if` and friends are `constexpr`, then the `Mata`
algorithms can be removed, and `std::` forms will just work.
That's a nice bonus.

Otherwise, we need something more like `boost::mpl`, which is
kinda annoying.  Still, `Meta::Container::vector` is very
nice -- it side-steps some issues with using `std::tuple` as
a type-list.
This commit is contained in:
ADAM David Alan Martin
2021-10-26 02:05:57 -04:00
parent 70a23059b0
commit 304640d76b
1 changed files with 5 additions and 3 deletions
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8
comparisons.h
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@ -33,10 +33,12 @@ namespace Alepha::Hydrogen
}
template< typename T >
constexpr bool has_comparable_capability_v= has_capability_v< std::decay_t< T >, comparable >;
constexpr bool has_comparable_capability_v= has_capability( Meta::type_value< std::decay_t< T > >{}, comparable_capability );
template< typename T >
struct has_comparable_capability : std::bool_constant< has_comparable_capability_v< T > > {};
struct has_comparable_capability_s : std::bool_constant< has_comparable_capability_v< T > > {};
inline constexpr Meta::trait< has_comparable_capability_s > has_comparable_capability;
// Spaceship lens support
@ -53,7 +55,7 @@ namespace Alepha::Hydrogen
template
<
typename T,
typename= std::enable_if_t< has_comparable_capability_v< T > >,
typename= std::enable_if_t< has_comparable_capability( Meta::type_value< T >{} ) >,
typename= std::enable_if_t< has_spaceship_lens_member_v< T > >,
overload< __LINE__ > = nullptr
>