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<p class="MsoNormal">Eventually, C++17 standard contracts may be used to specify these bounds checks. For now, we may use the same format but add them as comments or protected by macros; and when we switch to C++17 then these can be converted to actual contracts.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Proposal for contracts: <a href="http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2015/n4415.pdf">
http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2015/n4415.pdf</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Example contract:<o:p></o:p></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">T& operator[](size_t i) [[expects: i >= 0 && i < size()]];<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">For now, we could do this in VTK:<o:p></o:p></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">T& operator[](size_t i) VTK_CONTRACT([[expects: i >= 0 && i < size()]]);<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Andras<o:p></o:p></p>
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<p class="MsoNormal"><b>From:</b> David Gobbi [mailto:david.gobbi@gmail.com] <br>
<b>Sent:</b> Friday, August 4, 2017 4:05 PM<br>
<b>To:</b> Berk Geveci <berk.geveci@kitware.com><br>
<b>Cc:</b> Andras Lasso <lasso@queensu.ca>; VTK Developers <vtk-developers@vtk.org><br>
<b>Subject:</b> Re: [vtk-developers] Safer item access in Python wrapped VTK arrays<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">For a while, we kicked around the idea of having the hints in the comments. This would be less intrusive than adding C++11 attributes the declarations (i.e. what I've been doing so far).<o:p></o:p></p>
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<p class="MsoNormal">The C++11 attributes are definitely the cleanest way for the wrappers to store the hints, since the hints become part of the parse tree, so I want to keep them as the primary hinting mechanism. Comment-based hints could be added as a secondary
mechanism, i.e. after a declaration has been parsed we can check the docstring for extra hints, and then add the hints to the parse tree before the wrapper code is generated.<o:p></o:p></p>
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<p class="MsoNormal">I'll have to search through the archives to remember what kind of syntax we were considering for comment-based hints.<o:p></o:p></p>
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<p class="MsoNormal"> - David<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Fri, Aug 4, 2017 at 1:30 PM, Berk Geveci <<a href="mailto:berk.geveci@kitware.com" target="_blank">berk.geveci@kitware.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">As much as I support the concept of range checking in the wrappers, this hint will make things look very ugly and non-standard at a time where we are trying to move towards more standard looking C++. Isn't there a way of doing this without
mangling the signatures?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Fri, Aug 4, 2017 at 1:06 PM, David Gobbi <<a href="mailto:david.gobbi@gmail.com" target="_blank">david.gobbi@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Hi Andras,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Yes, this would be possible. It could be hard-coded into the wrappers, or even better, in the header file a generic hint could be added to the index parameter so that the index would be checked against the size of the array:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> float GetValue(vtkIdType idx VTK_RANGECHECK(0,GetNumberOfValues()));<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I have a list of wrapper hints at <a href="https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.vtk.org%2FWiki%2FVTK%2FWrapping_hints&data=02%7C01%7Classo%40queensu.ca%7C37f3749bcbbf4422f0ba08d4db741f07%7Cd61ecb3b38b142d582c4efb2838b925c%7C1%7C0%7C636374739163412038&sdata=FtQM8JHWrl8ReFwC3EFD4j0COBmWqm1r6k9b%2BF5tZzU%3D&reserved=0" target="_blank">http://www.vtk.org/Wiki/VTK/Wrapping_hints</a>,
and I can add this "RANGECHECK" hint to the "Proposed hints" section.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I'm hoping to find time to implement more of these wrapper hints over the next few weeks.<o:p></o:p></p>
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<p class="MsoNormal"><span style="color:#888888"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="color:#888888"> - David<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Fri, Aug 4, 2017 at 9:53 AM, Andras Lasso <<a href="mailto:lasso@queensu.ca" target="_blank">lasso@queensu.ca</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:#1F497D">Hi David,</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:#1F497D">Users who mostly use VTK via Python wrapping are sometimes surprised how easily they can crash the application by accessing out-of-bounds elements in
arrays. For example, this crashes an application:</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:8.5pt;font-family:Courier;color:black">>>>
</span><span style="font-size:8.5pt;font-family:Courier;color:#000096">a=vtk.vtkStringArray()</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:8.5pt;font-family:Courier;color:black">>>>
</span><span style="font-size:8.5pt;font-family:Courier;color:#000096">print(a.GetValue(0))</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:8.5pt;font-family:Courier;color:#000096"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:#1F497D">I first thought that it should be handled by documentation and training, but it would be nicer if the wrappers could handle this.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:#1F497D">Would it be feasible to add bounds check to VTK array accessors in Python wrappers, so that in case of an out of bounds access, a Python exception would
be raised instead of crashing the application?</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:#1F497D">Andras</span><span style="color:#888888"><o:p></o:p></span></p>
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