flann/util/any.h

#ifndef FLANN_ANY_H_
#define FLANN_ANY_H_
/*
 * (C) Copyright Christopher Diggins 2005-2011
 * (C) Copyright Pablo Aguilar 2005
 * (C) Copyright Kevlin Henney 2001
 *
 * Distributed under the Boost Software License, Version 1.0. (See
 * accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt
 *
 * Adapted for FLANN by Marius Muja
 */

#include <stdexcept>
#include <ostream>
#include <typeinfo>

namespace flann
{

namespace anyimpl
{

struct bad_any_cast : public std::runtime_error
{
	bad_any_cast() : std::runtime_error("Cannot convert 'any' value") { }
};

struct empty_any
{
};

inline std::ostream& operator <<(std::ostream& out, const empty_any&)
{
    out << "[empty_any]";
    return out;
}

struct base_any_policy
{
    virtual void static_delete(void** x) = 0;
    virtual void copy_from_value(void const* src, void** dest) = 0;
    virtual void clone(void* const* src, void** dest) = 0;
    virtual void move(void* const* src, void** dest) = 0;
    virtual void* get_value(void** src) = 0;
    virtual size_t get_size() = 0;
    virtual const std::type_info& type() = 0;
    virtual void print(std::ostream& out, void* const* src) = 0;
};

template<typename T>
struct typed_base_any_policy : base_any_policy
{
    virtual size_t get_size() { return sizeof(T); }
    virtual const std::type_info& type() { return typeid(T); }

};

template<typename T>
struct small_any_policy : typed_base_any_policy<T>
{
    virtual void static_delete(void**) { }
    virtual void copy_from_value(void const* src, void** dest)
    {
        new (dest) T(* reinterpret_cast<T const*>(src));
    }
    virtual void clone(void* const* src, void** dest) { *dest = *src; }
    virtual void move(void* const* src, void** dest) { *dest = *src; }
    virtual void* get_value(void** src) { return reinterpret_cast<void*>(src); }
    virtual void print(std::ostream& out, void* const* src) { out << *reinterpret_cast<T const*>(src); }
};

template<typename T>
struct big_any_policy : typed_base_any_policy<T>
{
    virtual void static_delete(void** x)
    {
        if (* x) delete (* reinterpret_cast<T**>(x)); *x = NULL;
    }
    virtual void copy_from_value(void const* src, void** dest)
    {
        *dest = new T(*reinterpret_cast<T const*>(src));
    }
    virtual void clone(void* const* src, void** dest)
    {
        *dest = new T(**reinterpret_cast<T* const*>(src));
    }
    virtual void move(void* const* src, void** dest)
    {
        (*reinterpret_cast<T**>(dest))->~T();
        **reinterpret_cast<T**>(dest) = **reinterpret_cast<T* const*>(src);
    }
    virtual void* get_value(void** src) { return *src; }
    virtual void print(std::ostream& out, void* const* src) { out << *reinterpret_cast<T const*>(*src); }
};

template<typename T>
struct choose_policy
{
    typedef big_any_policy<T> type;
};

template<typename T>
struct choose_policy<T*>
{
    typedef small_any_policy<T*> type;
};

struct any;

/// Choosing the policy for an any type is illegal, but should never happen.
/// This is designed to throw a compiler error.
template<>
struct choose_policy<any>
{
    typedef void type;
};

/// Specializations for small types.
#define SMALL_POLICY(TYPE) \
    template<> \
    struct choose_policy<TYPE> { typedef small_any_policy<TYPE> type; \
    }

SMALL_POLICY(signed char);
SMALL_POLICY(unsigned char);
SMALL_POLICY(signed short);
SMALL_POLICY(unsigned short);
SMALL_POLICY(signed int);
SMALL_POLICY(unsigned int);
SMALL_POLICY(signed long);
SMALL_POLICY(unsigned long);
SMALL_POLICY(float);
SMALL_POLICY(bool);

#undef SMALL_POLICY

/// This function will return a different policy for each type.
template<typename T>
base_any_policy* get_policy()
{
    static typename choose_policy<T>::type policy;
    return &policy;
}
} // namespace anyimpl

class any
{
	typedef any any_t; // workaround for the NVCC compiler under windows
private:
    // fields
    anyimpl::base_any_policy* policy;
    void* object;

public:
    /// Initializing constructor.
    template <typename T>
    any(const T& x)
        : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL)
    {
        assign(x);
    }

    /// Empty constructor.
    any()
        : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL)
    { }

    /// Special initializing constructor for string literals.
    any(const char* x)
        : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL)
    {
        assign(x);
    }

    /// Copy constructor.
    any(const any& x)
        : policy(anyimpl::get_policy<anyimpl::empty_any>()), object(NULL)
    {
        assign(x);
    }

    /// Destructor.
    ~any()
    {
        policy->static_delete(&object);
    }

    /// Assignment function from another any.
    any& assign(const any& x)
    {
        reset();
        policy = x.policy;
        policy->clone(&x.object, &object);
        return *this;
    }

    /// Assignment function.
    template <typename T>
    any_t& assign(const T& x)
    {
        reset();
        policy = anyimpl::get_policy<T>();
        policy->copy_from_value(&x, &object);
        return *this;
    }

    /// Assignment operator.
    template<typename T>
    any_t& operator=(const T& x)
    {
        return assign(x);
    }

    /// Assignment operator, specialed for literal strings.
    /// They have types like const char [6] which don't work as expected.
    any& operator=(const char* x)
    {
        return assign(x);
    }

    /// Utility functions
    any& swap(any& x)
    {
        std::swap(policy, x.policy);
        std::swap(object, x.object);
        return *this;
    }

    /// Cast operator. You can only cast to the original type.
    template<typename T>
    T& cast()
    {
        if (policy->type() != typeid(T)) throw anyimpl::bad_any_cast();
        T* r = reinterpret_cast<T*>(policy->get_value(&object));
        return *r;
    }

    /// Cast operator. You can only cast to the original type.
    template<typename T>
    const T& cast() const
    {
        if (policy->type() != typeid(T)) throw anyimpl::bad_any_cast();
        void* obj = const_cast<void*>(object);
        T* r = reinterpret_cast<T*>(policy->get_value(&obj));
        return *r;
    }

    /// Returns true if the any contains no value.
    bool empty() const
    {
        return policy->type() == typeid(anyimpl::empty_any);
    }

    /// Frees any allocated memory, and sets the value to NULL.
    void reset()
    {
        policy->static_delete(&object);
        policy = anyimpl::get_policy<anyimpl::empty_any>();
    }

    /// Returns true if the two types are the same.
    bool compatible(const any& x) const
    {
        return policy->type() == x.policy->type();
    }

    /// Returns if the type is compatible with the policy
    template<typename T>
    bool has_type()
    {
        return policy->type() == typeid(T);
    }

    const std::type_info& type() const
    {
        return policy->type();
    }

    friend std::ostream& operator <<(std::ostream& out, const any& any_val);
};

inline std::ostream& operator <<(std::ostream& out, const any& any_val)
{
    any_val.policy->print(out,&any_val.object);
    return out;
}

}

#endif // FLANN_ANY_H_