Load object from file design [closed] - c++

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What is the best design for loading an object from a file? There are lots of possibilities, some of which are shown below.
class object
{
public:
object(const std::string& filename);
};
class object
{
public:
object();
void load_from_file(const std::string& filename);
};
class object
{
public:
static object load_from_file(const std::string& filename);
object(object&& an_object);
};
class object
{
public:
std::unique_ptr<object> load_from_file(const std::string& filename);
};
class object_loader
{
public:
std::unique_ptr<object> load_object_from_file(const std::string& filename);
};
and the list goes on...
Edit:
The design I went with was this:
class object
{
public:
object();
};
class object_loader
{
public:
void load_from_stream(object& an_object, std::istream& input_stream);
};

Answer 1

I would prefer 'class object_loader' which separates the IO loader from the container, allowing future implementation of different loaders (from txt, binary, xml ... file) without modifying original data container. Better testing possible. Also possible to remove IO from app, if no IO allowed (like embedded devices, etc).

Answer 2

What is the best design for loading an object from a file?
The best design usually is along these lines:
class object { public: object(); /* ... */ }; // object is default constructible
std::istream& operator >> (std::istream& in, object& o);
client code:
// from file:
std::ifstream fin(path);
object o;
fin >> o;
// from serialized string:
std::string contents = ".....";
std::istrigstream ssin(contents);
ssin >> o;
Edit:
Transactional implementation:
std::istream& operator >> (std::istream& in, object& o)
{
int i; std::string word; // example data required by object instance
if (in >> i >> word)
{ // read was successful for all data
o.set_index(i);
o.set_word(word);
}
return in;
}
// client code:
if(ssin >> o)
{ // read was successful
// use o here
} else {
// o is still as default-constructed
}
This approach will work the same also if the stream throws exceptions on errors.