[Insight-developers] itk::VariableLengthVector (and probably other similer classes) allows boundless recursion in operators

[Bradley Lowekamp]

Kent,

I bet if you tried a ScalarImage as a template argument it would work as expected.

If disallow the case where:

template< typename TValueType, typename T >
inline
VariableLengthVector< TValueType >
operator*(const T & scalar, const VariableLengthVector< TValueType > & v)
{ return v * scalar; }

T is also of type variable length vector. Perhaps this would work:

template< typename TValueType, typename TValueType2 >
inline
VariableLengthVector< TValueType >
operator*(const VariableLengthVector< TValueType2 > & v, const VariableLengthVector< TValueType > & v); // Intentionally not implemented



On Feb 24, 2014, at 2:26 PM, Williams, Norman K <norman-k-williams at uiowa.edu> wrote:

> Logged as a bug; I'd write a patch if I can figure out how to do the C++ template metaprogramming magic.
> 
> I ran into this when I needed to multiply an itk::VectorImage by a scalar constant.  Using the MultiplyImageFilter, the SetConstant (and SetConstant1 and SetConstant2) methods only accept InputImage1PixelType as a constant. 
> 
> So, because I was deep into abstruse code, my naïve solution was to instantiate an itk::VariableLengthVector as the constant to pass to SetConstant, where each element was the scalar constant.
> 
> This is, upon further reflection, absurd, because A * B for vectors doesn't even make sense in matrix math, and there's no operator for pairwise multiplication of vector elements.
> 
> But what I found out running my program is that itk::VariableLengthVector will instantiate an operator * with boundless recursion.
> 
> There are two problems: not disallowing boundless recursion, and not supporting scalar constants for vector Images in itk::BinaryFunctorImageFilter.
> 
> https://issues.itk.org/jira/browse/SIMPLEITK-498
> 
> 
> 
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