diff options
Diffstat (limited to 'absl/container/internal/common_policy_traits.h')
| -rw-r--r-- | absl/container/internal/common_policy_traits.h | 45 |
1 files changed, 31 insertions, 14 deletions
diff --git a/absl/container/internal/common_policy_traits.h b/absl/container/internal/common_policy_traits.h index 0fd4866e..b42c9a48 100644 --- a/absl/container/internal/common_policy_traits.h +++ b/absl/container/internal/common_policy_traits.h @@ -63,7 +63,7 @@ struct common_policy_traits { // UNINITIALIZED template <class Alloc> static void transfer(Alloc* alloc, slot_type* new_slot, slot_type* old_slot) { - transfer_impl(alloc, new_slot, old_slot, 0); + transfer_impl(alloc, new_slot, old_slot, Rank0{}); } // PRECONDITION: `slot` is INITIALIZED @@ -80,29 +80,46 @@ struct common_policy_traits { return P::element(slot); } + static constexpr bool transfer_uses_memcpy() { + return std::is_same<decltype(transfer_impl<std::allocator<char>>( + nullptr, nullptr, nullptr, Rank0{})), + std::true_type>::value; + } + private: + // To rank the overloads below for overload resoltion. Rank0 is preferred. + struct Rank2 {}; + struct Rank1 : Rank2 {}; + struct Rank0 : Rank1 {}; + // Use auto -> decltype as an enabler. template <class Alloc, class P = Policy> static auto transfer_impl(Alloc* alloc, slot_type* new_slot, - slot_type* old_slot, int) + slot_type* old_slot, Rank0) -> decltype((void)P::transfer(alloc, new_slot, old_slot)) { P::transfer(alloc, new_slot, old_slot); } - template <class Alloc> - static void transfer_impl(Alloc* alloc, slot_type* new_slot, - slot_type* old_slot, char) { #if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606 - if (absl::is_trivially_relocatable<value_type>()) { - // TODO(b/247130232,b/251814870): remove casts after fixing warnings. - std::memcpy(static_cast<void*>( - std::launder(const_cast<std::remove_const_t<value_type>*>( - &element(new_slot)))), - static_cast<const void*>(&element(old_slot)), - sizeof(value_type)); - return; - } + // This overload returns true_type for the trait below. + // The conditional_t is to make the enabler type dependent. + template <class Alloc, + typename = std::enable_if_t<absl::is_trivially_relocatable< + std::conditional_t<false, Alloc, value_type>>::value>> + static std::true_type transfer_impl(Alloc*, slot_type* new_slot, + slot_type* old_slot, Rank1) { + // TODO(b/247130232): remove casts after fixing warnings. + // TODO(b/251814870): remove casts after fixing warnings. + std::memcpy( + static_cast<void*>(std::launder( + const_cast<std::remove_const_t<value_type>*>(&element(new_slot)))), + static_cast<const void*>(&element(old_slot)), sizeof(value_type)); + return {}; + } #endif + template <class Alloc> + static void transfer_impl(Alloc* alloc, slot_type* new_slot, + slot_type* old_slot, Rank2) { construct(alloc, new_slot, std::move(element(old_slot))); destroy(alloc, old_slot); } |