graphlab::any Class Reference

#include <any.hpp>

List of all members.

Public Member Functions
	any ()
	default constructor. Creates an empty any
template<typename ValueType >
	any (const ValueType &value)
	Creates an any which stores the value.
	any (const any &other)
bool	empty () const
	Returns true if the object does not contain any stored data.
const std::type_info &	type () const
	Returns the type information of the stored data.
void	load (iarchive &arc)
	loads the any from a file.
void	save (oarchive &arc) const
	Saves the any to a file. Caveats apply. See the main any docs.
template<typename ValueType >
ValueType &	as ()
	Extracts a reference to the contents of the any as a type of ValueType.
template<typename ValueType >
const ValueType &	as () const
	Extracts a constant reference to the contents of the any as a type of ValueType.
any &	swap (any &rhs)
	Exchanges the contents of two any's.
template<typename ValueType >
any &	operator= (const ValueType &rhs)
any &	operator= (const any &rhs)
std::ostream &	print (std::ostream &out) const

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Detailed Description

A generic "variant" object obtained from Boost::Any and modified to be serializable. A variable of type "any" can store any datatype (even dynamically changeable at runtime), but the caveat is that you must know the exact stored type to be able to extract the data safely.

To serialize/deserialize the any, regular serialization procedures apply. However, since a statically initialized type registration system is used to identify the type of the deserialized object, so the user must pay attention to a couple of minor issues.

On serialization:

• a) If an any contains a serializable type, the any can be serialized.
• b) If an any contains an unserializable type, the serialization will fail at runtime.

On deserialization:

• c) An empty any can be constructed with no type information and it can be deserialized from an archive.
• d) However, the deserialization will fail at runtime if the true type of the any is never accessed / instantiated anywhere in the code.

Condition d) is particular unusual so I will illustrate with an example.

Given a simple user struct:

   struct UserStruct {
     int i;
     void save (graphlab::oarchive& oarc) const {
       oarc << i;
     }
     void load (graphlab::iarchive& iarc) {
       iarc << i;
     }
   }

If an any object contains the struct, it will be serializable.

   UserStruct us;
   us.i = 10;
   any a = us;
   // output file
   std::ofstream fout("test.bin");
   graphlab::oarchive oarc(fout);
   oarc << a;    // write the any

To deserialize, I will open an input archive and stream into an any.

   // open input 
   std::ifstream fin("test.bin");
   graphlab::iarchive iarc(fin);
   // create an any and read it
   any a;
   iarc >> a; 

Now, unusually, the above code will fail, while the following code will succeed

   // open input 
   std::ifstream fin("test.bin");
   graphlab::iarchive iarc(fin);
   // create an any and read it
   any a;
   iarc >> a; 
   std::cout << a.as<UserStruct>().i;

The a.as<UserStruct>() forces the instantiation of static functions which allow the any deserialization to identify the UserStruct type.

Definition at line 172 of file any.hpp.

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The documentation for this class was generated from the following file:

• src/graphlab/util/generics/any.hpp