Thread: Copy Constructors

Do std::list/vector, boost::unorder_map, etc. have good copy constructors? or do I need to return by reference? if so, I guess that means I have to wrap them in shared_ptr's? what about shared_array?

This is sort of just an example...

Code:

typedef boost::unordered_map<std::string, std::string> Row;
typedef std::vector<Row> RowList;

RowList FetchRow();
RowList FetchRowList();

or

Code:

typedef boost::unordered_map<std::string, std::string> Row;
typedef std::vector<Row> RowList;

Row& FetchRow();
RowList& FetchRowList();

or

Code:

typedef boost::unordered_map<std::string, std::string> Row;
typedef std::vector<boost::shared_ptr<Row> > RowList;

Row FetchRowList();
RowList FetchRowList();

or

Code:

typedef boost::unordered_map<std::string, std::string> Row;
typedef std::vector<boost::shared_ptr<Row> > RowList;

Row& FetchRow();
RowList& FetchRowList();

or

Code:

typedef boost::unordered_map<std::string, std::string> Row;
typedef boost::shared_ptr<Row> pRow;
typedef std::vector<Row> RowList;

pRow FetchRow();
RowList FetchRowList();

or

Code:

typedef boost::unordered_map<std::string, std::string> Row;
typedef boost::shared_ptr<Row> pRow;
typedef std::vector<pRow> RowList;

pRow FetchRow();
RowList& FetchRowList();

or

Code:

typedef boost::unordered_map<std::string, std::string> Row;
typedef boost::shared_ptr<Row> pRow;
typedef std::vector<pRow> RowList;
typedef boost::shared_array<RowList> pRowList;

pRow FetchRow();
pRowList FetchRowList();

//pRowList r(new RowList); return r;

etc.

Last one?

Thanks guys!!

Originally Posted by Sebastiani

The efficiency of STL containers is dependant on how they're implemented. At any rate, generally speaking, you want to return references wherever possible, and by value if you don't want the return value altered. It might be a good idea to have the functions take references to a user-supplied variable to cut down on object-creation overhead.

Is the object creation overhead low with boost::shared_ptr? Would I need to take references to boost::shared_ptr, or just copies? or is it a thing where copies don't hurt, but references would be best (a benefit)?

Other than that, I got it. I wasn't sure I should go with the smart pointer approach. Actually I have to, since the function is creating the object itself rather than taking an argument. Otherwise references would be correct, allowing the user to control the object lifetime. Either way.

Thanks