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<xstd/bits/bit_concepts/bit_convertible_to.hpp>

bit_convertible_to

template<class From, class To>
concept bit_convertible_to = requires (From&& from) {
  { bit_convert<To>(std::forward<From>(from)) } -> same_as<remove_cv_t<To>>;
};
  • It holds exactly where bit_convert<To>(from) is valid: the positions map, though a source of run-time width may still throw. The source comes first, as in convertible_to, so bit_convertible_to<To> auto constrains a source.
  • A fixed width converts into one at least as wide: bit_fixed_set<64> to uint64_t, bitset<20> to bit_array<20>, array<uint8_t, 3> to bit_fixed_set<24>, bit_array<64> to bitset<64>, bit_set_view<uint64_t> to uint64_t, bit_array<5> to uint8_t, bit_fixed_set<64> to bit_fixed_set<65>, and uint64_t[4] to bit_array<256> and bitset<257>.
  • A run-time width converts into a fixed one: bit_set to uint64_t, bit_vector to bitset<70> and to bit_array<64>, bit_inplace_set<64> to bit_fixed_set<10>, and a bit_subspan window to bit_array<100>.
  • Anything converts into a run-time width: bit_span<array<uint8_t, 3>>, bit_array<64> and bit_span<vector<uint64_t>> to bit_vector, bitset<70> to bit_small_vector<64>, bit_vector to bit_inplace_set<64>, uint64_t to bit_set, and a window to bit_vector.
  • A reference or a const source is the conversion of the type it names: const bit_set& and bit_set&& to bit_vector. A cv-qualified target converts as the bare one: bit_array<64> to const uint64_t and to volatile bitset<64>, and bit_vector to const bit_set.
  • A volatile scalar converts by one read: volatile uint32_t& to bit_array<32>, and const volatile uint64_t& to bit_set.
  • Narrowing one fixed width into another would truncate, and is no conversion: bit_array<9> to uint8_t or const uint8_t, bit_fixed_set<65> to uint64_t, uint32_t to bit_array<20>, uint64_t to bitset<63>, bitset<65> to bit_array<64>, and uint64_t[4] to bit_array<255> are turned away.
  • A view is read from and never written into: uint64_t to bit_set_view<uint64_t>, and bit_vector to bit_span<array<uint8_t, 3>> or to a window, are turned away. So is a built-in array as a target, which no function returns: bit_array<256>, array<uint64_t, 4> and bit_vector to uint64_t[4].
  • What has no bit storage converts to nothing: vector<bool> to bit_vector, and bit_vector to vector<uint64_t>.
  • Volatile storage read by more than one access is no source: volatile bit_array<64>&, volatile bitset<64>&, volatile uint32_t(&)[2] and volatile array<uint32_t, 2>& are turned away.
  • With <xstd/bits/ext/boost/dynamic_bitset.hpp> included, boost::dynamic_bitset<> converts to bit_vector and uint64_t, bit_set and bitset<70> to boost::dynamic_bitset<>, and one boost::dynamic_bitset into another does not.