any.hxx

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/*               Copyright 2014-2015 by Ullrich Koethe                  */
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#pragma once

#ifndef VIGRA_ANY_HXX
#define VIGRA_ANY_HXX

#include "config.hxx"
#include "error.hxx"
#include <typeinfo>
#include <type_traits>

namespace vigra {

namespace detail {

struct AnyHandle
{
    AnyHandle() {}
    virtual ~AnyHandle() {}
    virtual const std::type_info & type() const = 0;
    virtual AnyHandle * clone() const = 0;
    virtual bool equal(AnyHandle const *) const = 0;

  private:
    AnyHandle(AnyHandle const &);
    AnyHandle & operator=(AnyHandle const &);
};

template <class T>
struct TypedAnyHandle
: public AnyHandle
{
    T value_;

    TypedAnyHandle(T const & t)
    : value_(t)
    {}

    const std::type_info & type() const
    {
        return typeid(T);
    }

    AnyHandle * clone() const
    {
        return new TypedAnyHandle(value_);
    }

    bool equal(AnyHandle const * h) const
    {
        TypedAnyHandle const * ptr = dynamic_cast<TypedAnyHandle const *>(h);
        return ptr != 0 && value_ == ptr->value_;
    }
};

struct ConvertibleAnyHandle
: public AnyHandle
{
    template <class T>
    struct TypeTag {};

    ConvertibleAnyHandle() {}

    virtual signed char      cast(TypeTag<signed char>) const = 0;
    virtual signed short     cast(TypeTag<signed short>) const = 0;
    virtual signed int       cast(TypeTag<signed int>) const = 0;
    virtual signed long      cast(TypeTag<signed long>) const = 0;
    virtual signed long long cast(TypeTag<signed long long>) const = 0;

    virtual unsigned char      cast(TypeTag<unsigned char>) const = 0;
    virtual unsigned short     cast(TypeTag<unsigned short>) const = 0;
    virtual unsigned int       cast(TypeTag<unsigned int>) const = 0;
    virtual unsigned long      cast(TypeTag<unsigned long>) const = 0;
    virtual unsigned long long cast(TypeTag<unsigned long long>) const = 0;

    virtual float       cast(TypeTag<float>) const = 0;
    virtual double      cast(TypeTag<double>) const = 0;
    virtual long double cast(TypeTag<long double>) const = 0;
};

#define VIGRA_ANY_OF_CONVERTIBLE(TYPE) \
template <> \
struct TypedAnyHandle<TYPE> \
: public ConvertibleAnyHandle \
{ \
    TYPE value_; \
    \
    TypedAnyHandle(TYPE const & t) \
    : value_(t) \
    {} \
    \
    const std::type_info & type() const \
    { \
        return typeid(value_); \
    } \
    \
    AnyHandle * clone() const \
    { \
        return new TypedAnyHandle(value_); \
    } \
    \
    bool equal(AnyHandle const * h) const \
    { \
        TypedAnyHandle const * ptr = dynamic_cast<TypedAnyHandle const *>(h); \
        return ptr != 0 && value_ == ptr->value_; \
    } \
    \
    virtual signed char      cast(TypeTag<signed char>) const \
    { return static_cast<signed char>(value_); } \
    virtual signed short     cast(TypeTag<signed short>) const \
    { return static_cast<signed short>(value_); } \
    virtual signed int       cast(TypeTag<signed int>) const \
    { return static_cast<signed int>(value_); } \
    virtual signed long      cast(TypeTag<signed long>) const \
    { return static_cast<signed long>(value_); } \
    virtual signed long long cast(TypeTag<signed long long>) const \
    { return static_cast<signed long long>(value_); } \
    \
    virtual unsigned char      cast(TypeTag<unsigned char>) const \
    { return static_cast<unsigned char>(value_); } \
    virtual unsigned short     cast(TypeTag<unsigned short>) const \
    { return static_cast<unsigned short>(value_); } \
    virtual unsigned int       cast(TypeTag<unsigned int>) const \
    { return static_cast<unsigned int>(value_); } \
    virtual unsigned long      cast(TypeTag<unsigned long>) const \
    { return static_cast<unsigned long>(value_); } \
    virtual unsigned long long cast(TypeTag<unsigned long long>) const \
    { return static_cast<unsigned long long>(value_); } \
    \
    virtual float       cast(TypeTag<float>) const \
    { return static_cast<float>(value_); } \
    virtual double      cast(TypeTag<double>) const \
    { return static_cast<double>(value_); } \
    virtual long double cast(TypeTag<long double>) const \
    { return static_cast<long double>(value_); } \
};

VIGRA_ANY_OF_CONVERTIBLE(signed char     )
VIGRA_ANY_OF_CONVERTIBLE(signed short    )
VIGRA_ANY_OF_CONVERTIBLE(signed int      )
VIGRA_ANY_OF_CONVERTIBLE(signed long     )
VIGRA_ANY_OF_CONVERTIBLE(signed long long)

VIGRA_ANY_OF_CONVERTIBLE(unsigned char     )
VIGRA_ANY_OF_CONVERTIBLE(unsigned short    )
VIGRA_ANY_OF_CONVERTIBLE(unsigned int      )
VIGRA_ANY_OF_CONVERTIBLE(unsigned long     )
VIGRA_ANY_OF_CONVERTIBLE(unsigned long long)

VIGRA_ANY_OF_CONVERTIBLE(float      )
VIGRA_ANY_OF_CONVERTIBLE(double     )
VIGRA_ANY_OF_CONVERTIBLE(long double)

#undef VIGRA_ANY_OF_CONVERTIBLE

} // namespace detail

    /** \brief Typesafe storage of arbitrary values.

        Items are always stored by value, but it is of course possible
        to store pointers and smart pointers.

        <b>Usage:</b>

        \code
        Any a(10);  // store integer '10'

        assert(a.is_type<int>());
        assert(a.is_convertible<int>());

        // retrieve the stored value (throws when types don't match)
        assert(a.get<int>() == 10);

        // change the value
        a = 20;
        assert(a.get<int>() == 20);

        // values of arithmetic types can be converted into each other
        // (this is currently not implemented for other types)
        assert(a.is_convewrtible<double>());
        assert(a.cast<double>() == 20.0);

        // delete the stored value
        a.destroy();
        assert(a.empty());
        assert(a == false);

        // store a shared_ptr
        typedef std::shared_ptr<int> Ptr;
        Any p(Ptr(new int(5))), q = p;
        assert(*(p.get<Ptr>()) == 5);
        // the addresses of the elements in p and q are the same
        assert(p.get<Ptr>().get() == p.get<Ptr>().get());
        \endcode
    */
class Any
{

    VIGRA_UNIQUE_PTR<detail::AnyHandle> handle_;

  public:

        /** Construct empty 'Any' object.
        */
    Any()
    : handle_((detail::AnyHandle*)0)
    {}

        /** Construct 'Any' object holding the given value.
        */
    template <class T>
    Any(T const & t)
    : handle_(new detail::TypedAnyHandle<T>(t))
    {}

        /** Construct 'Any' object holding a copy of other's value.
        */
    Any(Any const & other)
    : handle_(bool(other) ? other.handle_->clone() : (detail::AnyHandle*)0)
    {}

        /** Assign the given value to this 'Any' object
            (overwrites the old value, regardless of types).
        */
    template <class T>
    Any & operator=(T const & t)
    {
        handle_.reset(new detail::TypedAnyHandle<T>(t));
        return *this;
    }

        /** Assign a copy of other's value to this 'Any' object
            (overwrites the old value, regardless of types).
        */
    Any & operator=(Any const & other)
    {
        if(this != &other)
            handle_.reset(bool(other) ? other.handle_->clone() : (detail::AnyHandle*)0);
        return *this;
    }

        /** Delete the contained object (make this 'Any' object empty).
        */
    void destroy()
    {
        handle_.reset((detail::AnyHandle*)0);
    }

        /** Exchange the value of this object with other's.
        */
    void swap(Any & other)
    {
#ifdef VIGRA_NO_UNIQUE_PTR  // fallback for old compilers
        detail::AnyHandle *t = handle_.release(),
                          *o = other.handle_.release();
        handle_.reset(o);
        other.handle_.reset(t);
#else
        handle_.swap(other.handle_);
#endif
    }

        /** Exchange the value of objects l and r.
        */
    friend void swap(Any & l, Any & r)
    {
        l.swap(r);
    }

        /** Check if this object contains the same type and value as other.
            Also true if both 'Any' objects are empty.
        */
    bool operator==(Any const & other) const
    {
        return (handle_.get() == 0 && other.handle_.get() == 0) ||
               (handle_.get() != 0 && handle_->equal(other.handle_.get()));
    }

        /** Check if this object differs from other by type or value.
        */
    bool operator!=(Any const & other) const
    {
        return !operator==(other);
    }

    bool operator==(bool other) const
    {
        return bool(*this) == other;
    }

    bool operator!=(bool other) const
    {
        return bool(*this) != other;
    }

        /** Convert 'Any' to <tt>false</tt> if this object is empty, <tt>true</tt> otherwise.
        */
    operator bool() const
    {
        return handle_.get() != 0;
    }

        /** Check if this object is empty (holds no value).
        */
    bool empty() const
    {
        return handle_.get() == 0;
    }

        /** Check if this object holds a value of the given type.
        */
    template <class T>
    bool is_type() const
    {
        return dynamic_cast<detail::TypedAnyHandle<T> const *>(handle_.get()) != 0;
    }

        /** Check if this object's value is convertible to the given type.
            At present, this only succeeds if <tt>T</tt> matches the stored
            type exactly or is an arithmetic type convertible from the stored type.
        */
    template <class T>
    bool is_readable() const
    {
        return  (dynamic_cast<detail::TypedAnyHandle<T> const *>(handle_.get()) != 0) ||
                (std::is_arithmetic<T>::value &&
                 dynamic_cast<detail::ConvertibleAnyHandle const *>(handle_.get()) != 0);
    }

        /** Read-write access to the contained value. This throws an exception
            if the types don't match.
        */
    template <class T>
    T & get()
    {
        vigra_precondition(bool(*this), "Any::get(): object empty.");
        auto ptr = dynamic_cast<detail::TypedAnyHandle<T> *>(handle_.get());
        vigra_precondition(ptr != 0, "Any::get(): object is not an instance of the target type.");
        return ptr->value_;
    }

        /** Read-only access to the contained value. This throws an exception
            if the types don't match.
        */
    template <class T>
    T const & get() const
    {
        vigra_precondition(bool(*this), "Any::get(): object empty.");
        auto ptr = dynamic_cast<detail::TypedAnyHandle<T> const *>(handle_.get());
        vigra_precondition(ptr != 0, "Any::get(): object is not an instance of the target type.");
        return ptr->value_;
    }

        /** By-value access to the stored value. This throws an exception
            if the stored type doesn't match <tt>T</tt> and <tt>T</tt> is
            not an arithmetic type.
        */
    template <class T>
    T read() const
    {
        vigra_precondition(bool(*this), "Any::read(): object empty.");
        auto ptr1 = dynamic_cast<detail::TypedAnyHandle<T> const *>(handle_.get());
        if(ptr1 != 0)
            return ptr1->value_;
        auto ptr2 = dynamic_cast<detail::ConvertibleAnyHandle const *>(handle_.get());
        vigra_precondition(ptr2 != 0, "Any::read(): object is not covertible to the target type.");
        return ptr2->cast(detail::ConvertibleAnyHandle::TypeTag<T>());
    }
};

} // namespace vigra

#endif // VIGRA_ANY_HXX