rippled/modules/beast_basics/functor/beast_Function.h

//------------------------------------------------------------------------------
/*
    This file is part of Beast: https://github.com/vinniefalco/Beast
    Copyright 2013, Vinnie Falco <vinnie.falco@gmail.com>

    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.

    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================

#ifndef BEAST_FUNCTION_BEASTHEADER
#define BEAST_FUNCTION_BEASTHEADER

//
// Strong replacement for boost::function:
//
// #1 Bounded memory requirement, avoids the free store.
//
// #2 Always refers to a functor (i.e. is never invalid)
//
// #3 Default value (None) is a function that
//    returns a default object (the result type
//    constructed with a default constructor).
//

template <typename Signature, int Bytes = 128>
class Function;

//
// nullary function
//

template <typename R, int Bytes>
class Function <R (void), Bytes>
{
public:
    typedef R result_type;
    typedef Function self_type;

    struct None
    {
        typedef R result_type;
        result_type operator () () const
        {
            return result_type ();
        }
    };

    Function ()
    {
        constructCopyOf (None ());
    }

    Function (Function const& f)
    {
        f.getCall ().constructCopyInto (m_storage);
    }

    template <class Functor>
    Function (Functor const& f)
    {
        constructCopyOf (f);
    }

    ~Function ()
    {
        getCall ().~Call ();
    }

    Function& operator= (Function const& f)
    {
        getCall ().~Call ();
        f.getCall ().constructCopyInto (m_storage);
        return *this;
    }

    template <class Functor>
    Function& operator= (Functor const& f)
    {
        getCall ().~Call ();
        constructCopyOf (f);
        return *this;
    }

    result_type operator () ()
    {
        return getCall ().operator () ();
    }

private:
    template <class Functor>
    void constructCopyOf (Functor const& f)
    {
        // If this generates a compile error it means that
        // the functor is too large for the static buffer.
        // Increase the storage template parameter until
        // the error message goes away. This might cause
        // changes throughout the application with other
        // template classes that depend on the size.
        static_bassert (sizeof (StoredCall <Functor>) <= Bytes);
        new (m_storage) StoredCall <Functor> (f);
    }

private:
    struct Call
    {
        virtual ~Call () {}
        virtual void constructCopyInto (void* p) const = 0;
        virtual result_type operator () () = 0;
    };

    template <class Functor>
    struct StoredCall : Call
    {
        explicit StoredCall (Functor const& f) : m_f (f) { }
        StoredCall (const StoredCall& c) : m_f (c.m_f) { }
        void constructCopyInto (void* p) const
        {
            new (p) StoredCall (m_f);
        }
        result_type operator () ()
        {
            return m_f ();
        }
    private:
        Functor m_f;
    };

    Call& getCall ()
    {
        return *reinterpret_cast <Call*> (&m_storage[0]);
    }

    Call const& getCall () const
    {
        return *reinterpret_cast <Call const*> (&m_storage[0]);
    }

    char m_storage [Bytes]; // should be enough
};

//------------------------------------------------------------------------------

//
// unary function
//

template <typename R, typename T1, int Bytes>
class Function <R (T1 t1), Bytes>
{
public:
    typedef R result_type;
    typedef Function self_type;

    struct None
    {
        typedef R result_type;
        result_type operator () (T1) const
        {
            return result_type ();
        }
    };

    Function ()
    {
        constructCopyOf (None ());
    }

    Function (const Function& f)
    {
        f.getCall ().constructCopyInto (m_storage);
    }

    template <class Functor>
    Function (Functor const& f)
    {
        constructCopyOf (f);
    }

    ~Function ()
    {
        getCall ().~Call ();
    }

    Function& operator= (const Function& f)
    {
        getCall ().~Call ();
        f.getCall ().constructCopyInto (m_storage);
        return *this;
    }

    template <class Functor>
    Function& operator= (Functor const& f)
    {
        getCall ().~Call ();
        constructCopyOf (f);
        return *this;
    }

    result_type operator () (T1 t1)
    {
        return getCall ().operator () (t1);
    }

private:
    template <class Functor>
    void constructCopyOf (Functor const& f)
    {
        // If this generates a compile error it means that
        // the functor is too large for the static buffer.
        // Increase the storage template parameter until
        // the error message goes away. This might cause
        // changes throughout the application with other
        // template classes that depend on the size.
        static_bassert (sizeof (StoredCall <Functor>) <= Bytes);
        new (m_storage) StoredCall <Functor> (f);
    }

private:
    struct Call
    {
        virtual ~Call () {}
        virtual void constructCopyInto (void* p) const = 0;
        virtual result_type operator () (T1 t1) = 0;
    };

    template <class Functor>
    struct StoredCall : Call
    {
        explicit StoredCall (Functor const& f) : m_f (f) { }
        StoredCall (const StoredCall& c) : m_f (c.m_f) { }
        void constructCopyInto (void* p) const
        {
            new (p) StoredCall (m_f);
        }
        result_type operator () (T1 t1)
        {
            return m_f (t1);
        }
    private:
        Functor m_f;
    };

    Call& getCall ()
    {
        return *reinterpret_cast <Call*> (&m_storage[0]);
    }

    Call const& getCall () const
    {
        return *reinterpret_cast <Call const*> (&m_storage[0]);
    }

    char m_storage [Bytes]; // should be enough
};

#endif