Function preprocessMappedKey

fdbserver/storageserver.actor.cpp:4070–4104

create a vector of Optional in case of a singleKeyOrValue, insert an empty Tuple to vector as placeholder in case of a rangeQuery, insert Optional.empty as placeholder in other cases, insert the correct Tuple to be used.

// in case of a rangeQuery, insert Optional.empty as placeholder
// in other cases, insert the correct Tuple to be used.
void preprocessMappedKey(Tuple& mappedKeyFormatTuple, std::vector<Optional<Tuple>>& vt, bool& isRangeQuery) {
	vt.reserve(mappedKeyFormatTuple.size());

	for (int i = 0; i < mappedKeyFormatTuple.size(); i++) {
		Tuple::ElementType type = mappedKeyFormatTuple.getType(i);
		if (type == Tuple::BYTES || type == Tuple::UTF8) {
			std::string s = mappedKeyFormatTuple.getString(i).toString();
			auto sz = s.size();
			bool escaped = unescapeLiterals(s, "{{", "{");
			escaped = unescapeLiterals(s, "}}", "}") || escaped;
			if (escaped) {
				vt.emplace_back(Tuple::makeTuple(s));
			} else if (singleKeyOrValue(s, sz)) {
				// when it is SingleKeyOrValue, insert an empty Tuple to vector as placeholder
				vt.emplace_back(Tuple());
			} else if (rangeQuery(s)) {
				if (i != mappedKeyFormatTuple.size() - 1) {
					// It must be the last element of the mapper tuple
					throw mapper_bad_range_decriptor();
				}
				// when it is rangeQuery, insert Optional.empty as placeholder
				vt.emplace_back(Optional<Tuple>());
				isRangeQuery = true;
			} else {
				Tuple t;
				t.appendRaw(mappedKeyFormatTuple.subTupleRawString(i));
				vt.emplace_back(t);
			}
		} else {
			Tuple t;
			t.appendRaw(mappedKeyFormatTuple.subTupleRawString(i));
			vt.emplace_back(t);
		}
	}
}

Key constructMappedKey(KeyValueRef* keyValue,
                       std::vector<Optional<Tuple>>& vec,