any.h

/******************************************************************************
fast_any - A faster alternative to boost:any / std::any
Copyright (c) 2024, Marcus Tomlinson

BSD 2-Clause License

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

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FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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******************************************************************************/

#pragma once

#include <memory>

namespace fast_any
{

using type_info = unsigned int;
inline type_info type_info_seq = 1;
template <typename T>
inline const type_info type_id = type_info_seq++;

class any final
{
public:
    any();
    ~any();

    any( const any& other );
    any( any&& other );

    template <typename T>
    explicit any( const T& value );

    template <typename T>
    explicit any( T&& value );

    any& operator=( const any& other );
    any& operator=( any&& other );

    template <typename T>
    any& operator=( const T& value );

    template <typename T>
    any& operator=( T&& value );

    bool has_value() const;

    template <typename T>
    T* as() const;

    void emplace( const any& other );
    void emplace( any& other );
    void emplace( any&& other );

    template <typename T>
    void emplace( const T& value );

    template <typename T>
    void emplace( T&& value );

    void swap( any& other );

    void reset();

    type_info type() const;

private:
    struct value_holder_t
    {
        value_holder_t( const value_holder_t& ) = delete;
        value_holder_t& operator=( const value_holder_t& ) = delete;

        inline value_holder_t() = default;
        inline virtual ~value_holder_t() = default;

        inline virtual value_holder_t* clone() const = 0;
        inline virtual void emplace( const value_holder_t* value_holder ) = 0;
    };

    template <typename T>
    struct value_t final : value_holder_t
    {
        value_t() = delete;
        value_t( const value_t& ) = delete;
        value_t& operator=( const value_t& ) = delete;

        inline ~value_t() override = default;

        inline explicit value_t( const T& value )
            : value( value )
        {
        }

        inline explicit value_t( T&& value )
            : value( std::forward<T>( value ) )
        {
        }

        inline value_holder_t* clone() const override
        {
            return new value_t( value );
        }

        inline void emplace( const value_holder_t* value_holder ) override
        {
            value = reinterpret_cast<const value_t<T>*>( value_holder )->value;
        }

        T value;
    };

    value_holder_t* _value_holder = nullptr;
    bool _has_value = false;
    type_info _type = 0;
};

inline any::any() = default;

inline any::~any()
{
    delete _value_holder;
}

inline any::any( const any& other )
{
    emplace( other );
}

inline any::any( any&& other )
{
    emplace( std::forward<any>( other ) );
}

template <typename T>
inline any::any( const T& value )
{
    emplace( value );
}

template <typename T>
inline any::any( T&& value )
{
    emplace( std::forward<T>( value ) );
}

inline any& any::operator=( const any& other )
{
    emplace( other );
    return *this;
}

inline any& any::operator=( any&& other )
{
    emplace( std::forward<any>( other ) );
    return *this;
}

template <typename T>
inline any& any::operator=( const T& value )
{
    emplace( value );
    return *this;
}

template <typename T>
inline any& any::operator=( T&& value )
{
    emplace( std::forward<T>( value ) );
    return *this;
}

inline bool any::has_value() const
{
    return _has_value;
}

template <typename T>
inline T* any::as() const
{
    if ( _has_value && _type == type_id<T> )
    {
        return &reinterpret_cast<value_t<T>*>( _value_holder )->value;
    }
    else
    {
        return nullptr;
    }
}

inline void any::emplace( const any& other )
{
    _has_value = other._has_value;

    if ( _has_value )
    {
        if ( _type == other._type )
        {
            _value_holder->emplace( other._value_holder );
        }
        else
        {
            delete _value_holder;
            _value_holder = other._value_holder->clone();
            _type = other._type;
        }
    }
}

inline void any::emplace( any& other )
{
    _has_value = other._has_value;

    if ( _has_value )
    {
        if ( _type == other._type )
        {
            _value_holder->emplace( other._value_holder );
        }
        else
        {
            delete _value_holder;
            _value_holder = other._value_holder->clone();
            _type = other._type;
        }
    }
}

inline void any::emplace( any&& other )
{
    swap( other );
}

template <typename T>
inline void any::emplace( const T& value )
{
    _has_value = true;

    if ( _type == type_id<T> )
    {
        reinterpret_cast<value_t<T>*>( _value_holder )->value = value;
    }
    else
    {
        delete _value_holder;
        _value_holder = new value_t<T>( value );
        _type = type_id<T>;
    }
}

template <typename T>
inline void any::emplace( T&& value )
{
    _has_value = true;

    if ( _type == type_id<T> )
    {
        reinterpret_cast<value_t<T>*>( _value_holder )->value = std::forward<T>( value );
    }
    else
    {
        delete _value_holder;
        _value_holder = new value_t<T>( std::forward<T>( value ) );
        _type = type_id<T>;
    }
}

inline void any::swap( any& other )
{
    std::swap( other._value_holder, _value_holder );
    std::swap( other._has_value, _has_value );
    std::swap( other._type, _type );
}

inline void any::reset()
{
    _has_value = false;
}

inline type_info any::type() const
{
    if ( _has_value )
    {
        return _type;
    }
    else
    {
        return 0;
    }
}

}  // namespace fast_any