Concept checking whether key conversion through key_traits<K> is valid. More...

#include <jh/metax/lookup_map.h>

Concept definition

    template<typename K, typename T>
    concept transparent_key = requires(T t) {
        { jh::meta::extension::key_traits<K>::to_canonical(t) };
    }

Detailed Description

Concept checking whether key conversion through key_traits<K> is valid.

Enables heterogeneous lookup by verifying that an input type T can be converted into the canonical key type K through key_traits<K>::to_canonical(). This supports efficient zero-overhead implicit transformation for lightweight or compile-time strings.

Primary motivations:

Lookup tables should not store heavyweight or runtime-managed content.
Converted keys must remain low-cost and lifetime-stable.
jh::pod::string_view is recommended for string keys, usually via "..."_psv.
Compile-time helpers can convert std::string_view (including "..."sv literals) into jh::pod::string_view safely.
Design philosophy mirrors switch-like behavior: stable lifetime, direct literal use, and lightweight POD representations.

Template Parameters

K	Canonical key type of the lookup table.
T	Apparent input type to be checked for canonical conversion.

Note: This concept only checks convertibility; it does not validate semantics of the resulting canonical key.