Longer term solutions to DataContainer data type issue needed.

[evgueni-ovtchinnikov]

Some DataContainer methods compute a value that is complex for Gadgetron containers and real for other containers, and so, the variable that would store such a value cannot be explicitly declared in this abstract base class. Currently, this issue is quick-fixed by passing a void* to these methods that is cast to float* or complex_float_t* in the respective methods of the derived classes.

Possible longer term fixes:

• use the largest type in the C++ interface (i.e. std::complex) as opposed to void *. Easy, but probably unexpected.
• use std::any (and if needed with a virtual function std::any DataContainer::get_zero_data_element() or so). More complicated and not very elegant.
• template DataContainer if possible.

[evgueni-ovtchinnikov]

@KrisThielemans sorry not sure I understand your last suggestion:

• put a class in between RealDataContainer and ComplexDataContainer, which have the intuitive signatures, as well as the generic ones, which do all the ugly casting, such that the derived classes don't need to.

[KrisThielemans]

Something like this is probably better than what I had originally suggested as it needs only a template class, not 2 of them

template <typename DataType>
class DataContainerWithDataType: public DataContainer
{
public:
...
 virtual DataType sum() const = 0;
 virtual void sum(void * ptr) const override
 {
    const DataType ret = this->sum();
    *static_cast<DataType *>(ptr) = ret;
}


class STIRDataContainer : public DataContainerWithDataType<float>
{
private:
 typedef DataContainerWithDataType<float> base_type;
public:
  // make sure we get the generic version as well
  using  base_type::sum;
  virtual float sum() const override;
}