[Insight-developers] STYLE: Un-necessary use of static_cast -- should we care?

[Williams, Norman K]

Hans assigned me this ITK ticket to look into things:

https://itk.icts.uiowa.edu/jira/browse/ITK-2950


His feeling was that there were cases where dynamic_cast and checking the
returned pointer for 0 would be a more robust solution.

So I did an exhaustic examination of the use of static_cast in ITK.  This
amounted to 1408 (or more, sometimes they show up twice in the same line)
occurrences in ITK.

I pared this down to about half that many by eliminating casts to
intergral types, pointers to integral types. etc.

What I discovered is that there are many cases when static_cast is used
unnecessarily.  The most common being this idiom:

DataObject::Pointer returnDP()
{
  SomeDataObject::Pointer someData = SomeDataObject::New();
  return static_cast<DataObject *>(someData.GetPointer());
}

As SomeDataObject is always a class derived from DataObject, the return
value of someData.GetPointer() is assignment compatible with DataObject *

The only reason I can see to keep this usage is the idea that the
static_cast is for human eyes, not the compiler.

There's also a converse case, where dynamic_cast might do something useful:

template< class TOutputMesh >
typename MeshSource< TOutputMesh >::OutputMeshType *
MeshSource< TOutputMesh >
::GetOutput(void)
{
  return static_cast< TOutputMesh * >( this->GetPrimaryOutput() );
}

This assumes that the PrimaryOutput will in fact be of type TOutputMesh.
This may always be the case, but only because of programming discipline.
Both for GetInput and GetOutput, some faith is being placed in the filter
writers, but it isn't verified by compile-time type checking.

In those cases I can imagine that dynamic_cast + checking the returned
pointer might be a safer way to go.  On the other hand I just spent
several days dealing with the overhead of GetInput and GetOutput, and this
would only add to it.

So the question is this: do we keep static_cast where they aren't needed?
and should we add dynamic_cast in the frequent case where an input or
output of a filter is assumed to be of a particular type?





--
Kent Williams norman-k-williams at uiowa.edu






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