[Insight-users] ImageFunction Evaluate constness

[Dan Mueller]

Hi Insight community,

I am writing an ImageFunction for which the value depends on the image
point AND previous calls to the function.

To implement this I have added a member variable (a double) to my
subclassed image function. I want to set this member variable within:
    virtual TOutput Evaluate( const PointType& point ) const

I guess you can see my issue: Evaluate is marked const, so calls such as
    this->m_MemberVariable = 123.456;
do not compile. I get the following error with Visual Studio 2005:
    error C2166: l-value specifies const object

Of course I can get around this using const_cast on the this pointer:
    MyImageFunction<TInputImage,TOutput>* function =
      const_cast<MyImageFunction<TInputImage,TOutput>*>( this );
    function->m_MemberVariable = 123.456;

Some questions:
Am I abusing ImageFunction?
Does use of const_cast on the this pointer invoke the wrath of the
const-correctness police?
Is there a better way?

I guess I could create my own NonConstSingleThreadedImageFunction, but
then I'd bring the code-reuse police knocking...

Any suggestions appreciated.

Regards, Dan