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Make the in place std::variant<> extension smarter

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With the suggestions to use `std::get_if<>` and to only do this for
nontrivial types from
https://github.com/fraillt/bitsery/issues/76#issuecomment-850371533.
This commit is contained in:
Robbert van der Helm
2021-05-28 14:11:50 +02:00
parent 68d5d33cba
commit f533dd40ce
1 changed files with 16 additions and 12 deletions
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src/common/bitsery/ext/in-place-variant.h
+16 -12
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@@ -40,24 +40,28 @@ class InPlaceVariant : public StdVariant<Overloads...> {
des.adapter(), index, sizeof...(Ts),
std::integral_constant<bool, Des::TConfig::CheckDataErrors>{});
// Most of this is copied directly from the original implementation.
// We just added the check here to reuse the existing object if
// possible.
this->execIndex(index, obj, [this, &des](auto& data, auto index) {
constexpr size_t Index = decltype(index)::value;
using TElem =
typename std::variant_alternative<Index,
std::variant<Ts...>>::type;
// Most of this is copied directly from the original implementation.
// We just added the check here to reuse the existing object if
// possible.
if (std::holds_alternative<TElem>(data)) {
TElem& item = std::get<TElem>(data);
this->serializeType(des, item);
} else {
TElem item = ::bitsery::Access::create<TElem>();
this->serializeType(des, item);
data = std::variant<Ts...>(std::in_place_index_t<Index>{},
std::move(item));
// Reinitializing nontrivial types may be expensive especially when
// they reference heap data, so if `data` is already holding the
// requested variant then we'll deserialize into the existing object
if constexpr (std::is_trivial_v<TElem>) {
if (auto item = std::get_if<TElem>(&data)) {
this->serializeType(des, *item);
return;
}
}
TElem item = ::bitsery::Access::create<TElem>();
this->serializeType(des, item);
data = std::variant<Ts...>(std::in_place_index_t<Index>{},
std::move(item));
});
}
};