[Insight-users] dot product of itk vector was completely wrong

[Tim Allman]

This brings up an issue with respect to design in C++.

I have made far too many mistakes like this over the years, usually in 
my own code but with third party libraries as well. This strikes me as a 
constructor that was written as a "convenience" and the compiler happily 
tried to find a way of turning the returned scalar into a vector and 
made no complaints when it did.

I would probably not included this constructor at all because the 
following would do the same thing and the code would be clearer and less 
brittle. If it turned out to be useful I would have made it explicit.

...
itk::Vector<double, 3> vec;
vec.Fill(28.0);
...

I think C++ tries to be too friendly and it is too easy to write 
perfectly legal code which doesn't do what you expect.

Just a few thoughts,
Tim

On 14-02-11 07:54 PM, Bradley Lowekamp wrote:
> David,
>
> Thanks for updating the Wiki Examples.
>
> Brad
>
> On Feb 11, 2014, at 3:45 PM, David Doria <daviddoria at gmail.com> wrote:
>
>> On Tue, Feb 11, 2014 at 3:04 PM, Bradley Lowekamp
>> <blowekamp at mail.nih.gov> wrote:
>>> http://www.itk.org/Doxygen/html/classitk_1_1Vector.html
>>>
>>> The return type for the operator* for a dot product is Vector::ValueType, a
>>> scalar, not a vector.
>>> http://www.itk.org/Doxygen/html/classitk_1_1Vector.html#a51bad5a3835ffc0fbbc02d5437f7e691
>>>
>>> By assigning to to a new Vector are implicitly calling this constructor:
>>> http://www.itk.org/Doxygen/html/classitk_1_1Vector.html#a106ee9550311054cceb66015e98c6457
>>>
>>> The example is wrong. Watch your types.
>>>
>>> Brad
>> Brad is right - the 'dotproduct' variable in the example should be a
>> VectorType::ComponentType, not just VectorType. I updated the page
>> with the fix.
>>
>> David
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-- 
Tim Allman, Ph.D.
35 Margaret Street,
Guelph Ontario N1E 5R6
Canada

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