Signal.h

/******************************************************************************
DSPatch - The Refreshingly Simple C++ Dataflow Framework
Copyright (c) 2020, 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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#pragma once
 
#include <dspatch/Common.h>
 
namespace DSPatch
{
 
 
class DLLEXPORT Signal final
{
public:
    NONCOPYABLE( Signal );
    DEFINE_PTRS( Signal );
 
    Signal();
    ~Signal();
 
    bool HasValue() const;
 
    template <class ValueType>
    ValueType* GetValue();
 
    template <class ValueType>
    void SetValue( ValueType const& newValue );
 
    bool CopySignal( Signal::SPtr const& fromSignal );
    bool MoveSignal( Signal::SPtr const& fromSignal );
 
    void ClearValue();
 
    std::type_info const& GetType() const;
 
private:
    struct _ValueHolder
    {
        NONCOPYABLE( _ValueHolder );
 
        _ValueHolder() = default;
        virtual ~_ValueHolder() = default;
 
        virtual std::type_info const& GetType() const = 0;
        virtual _ValueHolder* GetCopy() const = 0;
        virtual void SetValue( _ValueHolder* valueHolder ) = 0;
    };
 
    template <class ValueType>
    struct _Value final : _ValueHolder
    {
        NONCOPYABLE( _Value );
 
        _Value( ValueType const& value )
            : value( value )
            , type( typeid( ValueType ) )
        {
        }
 
        virtual std::type_info const& GetType() const override
        {
            return type;
        }
 
        virtual _ValueHolder* GetCopy() const override
        {
            return new _Value( value );
        }
 
        virtual void SetValue( _ValueHolder* valueHolder ) override
        {
            value = ( (_Value<ValueType>*)valueHolder )->value;
        }
 
        ValueType value;
        std::type_info const& type;
    };
 
    _ValueHolder* _valueHolder = nullptr;
    bool _hasValue = false;
};
 
template <class ValueType>
ValueType* Signal::GetValue()
{
    // You might be thinking: Why the raw pointer return here?
 
    // This is mainly for performance, and partly for readability. Performance, because returning a
    // shared_ptr here means having to store the value as a shared_ptr in Signal::_Value too. This
    // adds yet another level of indirection to the value, as well as some reference counting
    // overhead. These Get() and Set() methods are VERY frequently called, so doing as little as
    // possible with the data here is best, which actually aids in the readably of the code too.
 
    if ( _hasValue && GetType() == typeid( ValueType ) )
    {
        return &( (_Value<ValueType>*)_valueHolder )->value;
    }
    else
    {
        return nullptr;
    }
}
 
template <class ValueType>
void Signal::SetValue( ValueType const& newValue )
{
    if ( GetType() == typeid( ValueType ) )
    {
        ( (_Value<ValueType>*)_valueHolder )->value = newValue;
    }
    else
    {
        delete _valueHolder;
        _valueHolder = new _Value<ValueType>( newValue );
    }
    _hasValue = true;
}
 
}  // namespace DSPatch