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

[Williams, Norman K]

That does work.

I'm concerned that this doesn't generate any error and warning and then goes into boundless recursion at runtime:

itk::VariableLengthVector<double> a(3);
a[0] = 1; a[1] = 2; a[2] = 3;
a = a * a;

There are two operator* in VariableLengthVector: a member function and a template function. The template function should be prevented from instantiating in this case.


From: Bradley Lowekamp <blowekamp at mail.nih.gov<mailto:blowekamp at mail.nih.gov>>
Date: Monday, February 24, 2014 4:13 PM
To: Mushly McMushmaster <norman-k-williams at uiowa.edu<mailto:norman-k-williams at uiowa.edu>>
Cc: ITK <insight-developers at itk.org<mailto:insight-developers at itk.org>>
Subject: Re: [Insight-developers] itk::VariableLengthVector (and probably other similer classes) allows boundless recursion in operators

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<mailto: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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