Implicit vs. explicit

[lni]

Hi,

Is there an QVector replacement for explicit sharing?

Currently I am using QVector<float>, but it calls detach() when data() is called. If there a way not to call detach()? In another word, I need explicit sharing QVector.

Thanks

[wysota]

There is no such replacement. You can only pass references to the vector instead of copies of it everywhere.

[lni]

There is no such replacement. You can only pass references to the vector instead of copies of it everywhere.

I have to pass value of QVector<float>, at the same time I want to change value in one vector and all others get the same change.

Currently I do like this:

const float* data = vector.constData(); // <- doesn't call detach()
((float*)data)[ 3 ] = 5.6; // <- hard cast...

I know this is a very bad idea, but it is the only way not to call detach() and prevent copy on the write...

Any better idea?

[scascio]

Why not using shared pointers, from boost or some other lib?

[lni]

I end up creating my own shared array using QVector

template <typename Type>
class QfwSharedArray
{
public:
 
  QfwSharedArray() : d( new QfwSharedArrayData ) {
  }
 
  QfwSharedArray( const QVector<Type>& array ) : d( new QfwSharedArrayData ) {
    setArray( array );
  }
 
  QfwSharedArray( const QfwSharedArray& org ) : d( org.d ) {
  }
 
  ~QfwSharedArray() {
  }
 
  QfwSharedArray& operator=( const QfwSharedArray& rhs ) {
    d = rhs.d;
    return *this;
  }
 
  bool operator==( const QfwSharedArray& rhs ) const {
    return d == rhs.d;
  }
 
  bool operator!=( const QfwSharedArray& rhs ) const {
    return !operator==( rhs );
  }
 
  const QVector<Type>& array() const {
    return d->array;
  }
  QVector<Type>& array() {
    return d->array;
  }
 
  int size() const {
    return d->array.size();
  }
 
  void resize( int size ) {
    d->array.resize( size );
  }
 
  void setArray( const QVector<Type>& array ) {
    d->array = array;
  }
 
  operator QVector<Type>&() {
    return d->array;
  }
 
  operator const QVector<Type>&() const {
    return d->array;
  }
 
  QVector<Type>& operator() () {
    return d->array;
  }
 
  const QVector<Type>& operator() () const {
    return d->array;
  }
 
  Type &operator[]( int i ) {
    return d->array[ i ];
  }
 
  const Type &operator[]( int i ) const {
    return d->array[ i ];
  }
 
private:
 
  class QfwSharedArrayData : public QSharedData {
    public:
      QVector<Type>       array;
  };
 
  QExplicitlySharedDataPointer<QfwSharedArrayData> d;
 
};
 
template <typename Type>
QDebug operator<<( QDebug dbg, const QfwSharedArray<Type>& sa ) {
  dbg.nospace() << sa.array();
  return dbg.nospace();
}

template <typename Type>
class QfwSharedArray
{
public:

  QfwSharedArray() : d( new QfwSharedArrayData ) {
  }

  QfwSharedArray( const QVector<Type>& array ) : d( new QfwSharedArrayData ) {
    setArray( array );
  }

  QfwSharedArray( const QfwSharedArray& org ) : d( org.d ) {
  }

  ~QfwSharedArray() {
  }

  QfwSharedArray& operator=( const QfwSharedArray& rhs ) {
    d = rhs.d;
    return *this;
  }

  bool operator==( const QfwSharedArray& rhs ) const {
    return d == rhs.d;
  }

  bool operator!=( const QfwSharedArray& rhs ) const {
    return !operator==( rhs );
  }

  const QVector<Type>& array() const {
    return d->array;
  }
  QVector<Type>& array() {
    return d->array;
  }

  int size() const {
    return d->array.size();
  }

  void resize( int size ) {
    d->array.resize( size );
  }

  void setArray( const QVector<Type>& array ) {
    d->array = array;
  }

  operator QVector<Type>&() {
    return d->array;
  }

  operator const QVector<Type>&() const {
    return d->array;
  }

  QVector<Type>& operator() () {
    return d->array;
  }

  const QVector<Type>& operator() () const {
    return d->array;
  }

  Type &operator[]( int i ) {
    return d->array[ i ];
  }

  const Type &operator[]( int i ) const {
    return d->array[ i ];
  }

private:

  class QfwSharedArrayData : public QSharedData {
    public:
      QVector<Type>       array;
  };

  QExplicitlySharedDataPointer<QfwSharedArrayData> d;

};

template <typename Type>
QDebug operator<<( QDebug dbg, const QfwSharedArray<Type>& sa ) {
  dbg.nospace() << sa.array();
  return dbg.nospace();
}

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