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POVariant implementation like boost::any with auto-conversion support
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2011-09-06T07:55:29.750
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2011-09-06T12:33:21.980
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2011-09-06T12:33:21.980
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I want to implement a variant class that can store any datatype (like boost::any) but with the support of datatype conversion. For example, <pre><code>Variant v1(int(23)); can be converted to bool via v1.get<bool>() using Conv<int, bool>, Variant v2(CustomT1()); to CustomT2 via Conv<CustomT1, CustomT2> and so on. </code></pre> Here is the current implementation, based on the idea of boost::any: <pre><code>#include <iostream> #include <string> #include <memory> #include <stdexcept> template<typename Src, typename Dest> struct Conv { /* static? */ Dest convert(const Src& src) const { throw std::runtime_error("type cast not supported"); } }; template<> struct Conv<int, bool> { bool convert(const int &src) const { return src > 0; } }; class IStoredVariant {}; template<typename T> struct variant_storage : public IStoredVariant { variant_storage(const T& value) : m_value(value) {} T& getValue(void) { return this->m_value; } const T& getValue(void) const { return this->m_value; } template<typename U> U make_conversion(void) const // just an idea... { return Conv<U, T>().convert(this->getValue()); } protected: T m_value; }; class Variant { public: template<typename T> Variant(const T& value) : m_storage(new variant_storage<T>(value)) {} IStoredVariant& getImpl(void) { return *this->m_storage; } const IStoredVariant& getImpl(void) const { return *this->m_storage; } std::auto_ptr<IStoredVariant> m_storage; template<typename T> T get(void) const { const IStoredVariant &var = this->getImpl(); // ???????????? // How to perform conversion? } template<typename T> void set(const T &value) { this->m_storage.reset(new variant_storage<T>(value)); } }; int main(void) { Variant v(int(23)); bool i = v.get<bool>(); } </code></pre> From the get<> template method, I only have access to an IStoredVariant pointer, but I need to know the concrete type to choose the Converter<>. Is there any design pattern or workaround to solve this problem?
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Variant implementation like boost::any with auto-conversion support
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1. COYou might want to use `boost::variant` as the basis, since that will remember which type is contained. This information is essential ;v) .
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