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What are the advantages of using boost.any library ? Could you please give me some real life examples ? Why the same functionality couldn't be achieved by having some generic type in the root of object's hierarchy and creating containers with that base type ?
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The key difference between boost::any and boost::variant is that any can store any type, while variant can store only one of a set of enumerated types. The any type stores a void* pointer to the object, as well as a typeinfo object to remember the underlying type and enforce some degree of type safety.
The Boost PP library supports four individual high-level data types. These are arrays, lists, seqs, and tuples.
The boost::any class (based on the class of the same name described in "Valued Conversions" by Kevlin Henney, C++ Report 12(7), July/August 2000) is a variant value type based on the second category. It supports copying of any value type and safe checked extraction of that value strictly against its type.
boost::variant is defined in boost/variant. hpp . Because boost::variant is a template, at least one parameter must be specified. One or more template parameters specify the supported types. In Example 24.1, v can store values of type double , char , or std::string .
boost::any will happily store ints and floats, types that clearly have no base classes. A real-life example where you can use it is a virtual machine for a high-level interpreted language. Your "function" objects will need an array of arguments. This can easily be implemented with a std::list<boost::any> behind the scenes.
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I consider that Boost.Variant should always be preferred as it's non-intrusive and still calls for very structured programming.
But i guess the main idea behind boost.any is to provide the equivalent of java and c# object types. It's a way of saying "yes we can" ! :-)
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