Wrapper with signals for primitive types

G_ka

Hi,
I'd like to create a wrapper for primitive types, that would emit a signal when the value is changed and have a slot to change the value.The obvious way would be to use a template class:

template<typename Type>
class QValueWrapper : public QObject
{
    Q_OBJECT

signals:
    void valueChanged(Type newValue);

public:
    void setValue(const Type &newValue)
    {
        if(value_ != newValue)
            emit valueChanged(newValue);
        value_ = newValue;
    }

private: 
    Type value_;
};

But Qt signals does not support template classes. So how would you do it? I'd like to avoid creating a wrapper for each value type, if possible
Thanks

VRonin

But Qt signals does not support template classes.

this is not strictly correct. It's MOC that can't cope with templates.

You have 3 alternatives that I can think of:

QVariant as correctly pointed out by @mcleary
bypass MOC using Verdigris

#include <wobjectdefs.h>
#include <wobjectimpl.h>
template<typename Type>
class QValueWrapper : public QObject
{
    W_OBJECT(QValueWrapper )
public:
    QValueWrapper(QObject* parent = nullptr) :QObject(parent){};
    QValueWrapper(const Type & val,QObject* parent = nullptr) : QObject(parent), value_(val){}
    void valueChanged(Type newValue);
    W_SIGNAL(valueChanged, newValue)
    const Type & value() const {return value_;}
    void setValue(const Type &newValue)
    {
        if(value_ != newValue)
            emit valueChanged(newValue);
        value_ = newValue;
    }
    W_SLOT(setValue)
private: 
    Type value_;
};
W_OBJECT_IMPL(QValueWrapper <Type>, template <typename Type>)

move the signal to a template-less qobject

class QValueWrapperHelper : public QObject
{
    Q_OBJECT
public:
QValueWrapperHelper(QObject* parent = nullptr) :QObject(parent){};
signals:
    void valueChanged();
};

template<typename Type>
class QValueWrapper : public QValueWrapperHelper 
{
public:
QValueWrapper(QObject* parent = nullptr) :QValueWrapperHelper(parent){};
QValueWrapper(const Type & val,QObject* parent = nullptr) :QValueWrapperHelper(parent), value_(val){};
const Type & value() const {return value_;}
    void setValue(const Type &newValue)
    {
        if(value_ != newValue)
            emit valueChanged();
        value_ = newValue;
    }
private: 
    Type value_;
};

mcleary

The first thing that comes to my mind is to use a QVariant to store the value you want. QVariant supports all primitive types.

VRonin

But Qt signals does not support template classes.

this is not strictly correct. It's MOC that can't cope with templates.

You have 3 alternatives that I can think of:

QVariant as correctly pointed out by @mcleary
bypass MOC using Verdigris

#include <wobjectdefs.h>
#include <wobjectimpl.h>
template<typename Type>
class QValueWrapper : public QObject
{
    W_OBJECT(QValueWrapper )
public:
    QValueWrapper(QObject* parent = nullptr) :QObject(parent){};
    QValueWrapper(const Type & val,QObject* parent = nullptr) : QObject(parent), value_(val){}
    void valueChanged(Type newValue);
    W_SIGNAL(valueChanged, newValue)
    const Type & value() const {return value_;}
    void setValue(const Type &newValue)
    {
        if(value_ != newValue)
            emit valueChanged(newValue);
        value_ = newValue;
    }
    W_SLOT(setValue)
private: 
    Type value_;
};
W_OBJECT_IMPL(QValueWrapper <Type>, template <typename Type>)

move the signal to a template-less qobject

class QValueWrapperHelper : public QObject
{
    Q_OBJECT
public:
QValueWrapperHelper(QObject* parent = nullptr) :QObject(parent){};
signals:
    void valueChanged();
};

template<typename Type>
class QValueWrapper : public QValueWrapperHelper 
{
public:
QValueWrapper(QObject* parent = nullptr) :QValueWrapperHelper(parent){};
QValueWrapper(const Type & val,QObject* parent = nullptr) :QValueWrapperHelper(parent), value_(val){};
const Type & value() const {return value_;}
    void setValue(const Type &newValue)
    {
        if(value_ != newValue)
            emit valueChanged();
        value_ = newValue;
    }
private: 
    Type value_;
};

G_ka

Thanks to both of you. I think I will use your third solution, @VRonin
I'll mark this topic as solved as soon as I try it