As discussed with @kitaisreal 
: columns(other.columns)
    , secondary_indices(other.secondary_indices)
    , constraints(other.constraints)
    , projections(other.projections.clone())
    , partition_key(other.partition_key)
    , primary_key(other.primary_key)
    , sorting_key(other.sorting_key)
    , sampling_key(other.sampling_key)
    , column_ttls_by_name(other.column_ttls_by_name)
    , table_ttl(other.table_ttl)
    , settings_changes(other.settings_changes ? other.settings_changes->clone() : nullptr)
    , select(other.select)
    , comment(other.comment)
{
}
StorageInMemoryMetadata & StorageInMemoryMetadata::operator=(const StorageInMemoryMetadata & other)