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## Function any_cast

boost::type_erasure::any_cast

## Synopsis

    // In header: <boost/type_erasure/any_cast.hpp>

    template<typename T, typename Concept, typename Tag>
      T any_cast(any< Concept, Tag > & arg);
    template<typename T, typename Concept, typename Tag>
      T any_cast(const any< Concept, Tag > & arg);
    template<typename T, typename Concept, typename Tag>
      T any_cast(any< Concept, Tag > * arg);
    template<typename T, typename Concept, typename Tag>
      T any_cast(const any< Concept, Tag > * arg);

## Description

Attempts to extract the object that `arg` holds. If casting to a pointer fails, `any_cast` returns a null pointer. Casting to `void*` always succeeds and returns the address of stored object.

    any<mpl::vector<typeid_<>, copy_constructible<> > > x(1);
    any_cast<int>(x);      // returns 1
    any_cast<int&>(x);     // returns a reference to the contents of x
    any_cast<double>(x);   // throws bad_any_cast
    any_cast<int*>(&x);    // returns a pointer to the contents of x
    any_cast<void*>(&x);   // returns a pointer to the contents of x
    any_cast<double*>(&x); // returns NULL

Requires: | if `arg` is a pointer, `T` must be a pointer type.
Requires: | `Concept` must contain typeid_``<Tag>.
Throws: | bad_any_cast if `arg` doesn't contain an object of type `T` and we're casting to a value or reference.