so whether tuple_cat works with tuple-like types is implementation defined,
apply doesn't work with them period (except standard tuple-likes),
and make_from_tuple apparently is like apply in c++17, but is supposed to work with them in c++20, and yet no implementation complies... I must know who is responsible for this! some pussy ass library vendor no doubt >:(
also not a fan of these pure code specs in the standard (apply and make_from_tuple), spelling it all out in english they probably would've avoided these weird inconsistencies... reminds me of some video codec specs, where it feels like they just copy pasted the implementation: "there ya go, cryptic c code, that's your spec"...