This is a polymorphic wrapper capable of holding any type. (It is loosely based onboost::any)

In particular, this is useful when you want to store a heterogeneous collection, such asvector<Any>.

Synopsis

string s = ...;int i = ...;Any a1 = s;Any a2 = i;int j = a2; // ok j now equals istring t = a1; // ok t now equals sint k = a1; // runtime exception bad_castvector<Any> v;v.push_back("foo");v.push_back(42);const char* s = v[0];int l = v[1];

Implementation

#include <type_traits>#include <utility>#include <typeinfo>#include <string>#include <cassert>using namespace std;template<class T>using StorageType = typename decay<typename remove_reference<T>::type>::type;struct Any{    bool is_null() const { return !ptr; }    bool not_null() const { return ptr; }    template<typename U> Any(U&& value)        : ptr(new Derived<StorageType<U>>(forward<U>(value)))    {    }    template<class U> bool is() const    {        typedef StorageType<U> T;        auto derived = dynamic_cast<Derived<T>*> (ptr);        return derived;    }    template<class U>    StorageType<U>& as()    {        typedef StorageType<U> T;        auto derived = dynamic_cast<Derived<T>*> (ptr);        if (!derived)            throw bad_cast();        return derived->value;    }    template<class U>    operator U()    {        return as<StorageType<U>>();    }    Any()        : ptr(nullptr)    {    }    Any(Any& that)        : ptr(that.clone())    {    }    Any(Any&& that)        : ptr(that.ptr)    {        that.ptr = nullptr;    }    Any(const Any& that)        : ptr(that.clone())    {    }    Any(const Any&& that)        : ptr(that.clone())    {    }    Any& operator=(const Any& a)    {        if (ptr == a.ptr)            return *this;        auto old_ptr = ptr;        ptr = a.clone();        if (old_ptr)            delete old_ptr;        return *this;    }    Any& operator=(Any&& a)    {        if (ptr == a.ptr)            return *this;        swap(ptr, a.ptr);        return *this;    }    ~Any()    {        if (ptr)            delete ptr;    }private:    struct Base    {        virtual ~Base() {}        virtual Base* clone() const = 0;    };    template<typename T>    struct Derived : Base    {        template<typename U> Derived(U&& value) : value(forward<U>(value)) { }        T value;        Base* clone() const { return new Derived<T>(value); }    };    Base* clone() const    {        if (ptr)            return ptr->clone();        else            return nullptr;    }    Base* ptr;};

Test

int main(){    Any n;    assert(n.is_null());    string s1 = "foo";    Any a1 = s1;    assert(a1.not_null());    assert(a1.is<string>());    assert(!a1.is<int>());    Any a2(a1);    assert(a2.not_null());    assert(a2.is<string>());    assert(!a2.is<int>());    string s2 = a2;    assert(s1 == s2);}

• 1
  \$\begingroup\$This seems not compiling on Visual Studio 2010... anybody tried on VS 2010?\$\endgroup\$

  Dan Niero

  – Dan Niero

  2013-08-21 08:36:22 +00:00

  CommentedAug 21, 2013 at 8:36
• 2
  \$\begingroup\$@DanNiero The C++11 support in Visual Studio (especially the 2010 version) is incomplete. It lacks various features including template aliases (which, I think, the 2012 version lacks as well), so you won't get this code to compile in Visual Studio.\$\endgroup\$

  sepp2k

  – sepp2k

  2013-08-21 13:07:35 +00:00

  CommentedAug 21, 2013 at 13:07
• \$\begingroup\$Does it compile with VS2012? At least, not on my side. I've received a lot of compilation errors.\$\endgroup\$

  user32438

  – user32438

  2013-11-21 14:54:51 +00:00

  CommentedNov 21, 2013 at 14:54
• \$\begingroup\$What's your license on this code?\$\endgroup\$

  user7535

  – user7535

  2014-04-21 06:34:25 +00:00

  CommentedApr 21, 2014 at 6:34
• 2
  \$\begingroup\$@DigitalArchitect: Public domain. You may use it any way you like without attribution.\$\endgroup\$

  user1131146 account abandoned

  – user1131146 account abandoned

  2014-04-21 06:39:33 +00:00

  CommentedApr 21, 2014 at 6:39

2 Answers2

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