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IDProjectCategoryView StatusDate SubmittedLast Update
0007192VTK(No Category)public2008-06-14 17:432016-08-12 09:54
ReporterTom Fogal 
Assigned ToKitware Robot 
PrioritynormalSeverityminorReproducibilityalways
StatusclosedResolutionmoved 
PlatformOSOS Version
Product Version 
Target VersionFixed in Version 
Project
Type
Summary0007192: Read-only access to objects is not const correct
DescriptionAccessing data within a VTK object is a mutable operation, even when the data access itself does not actually mutate the object's state. This imposes difficulties when using VTK in a const-correct environment.
Steps To Reproduce
Additional InformationAttached is a small patch aimed at allowing easier use of VTK in a const correct program. The current definition of vtkGetObjectMacro essentially expands into:
    virtual type *GetWhateverYouSay() { ... }
This causes the macro to expand into:
    virtual type *GetWhateverYouSay() { ... }
    virtual const type *GetWhateverYouSay() const { ... }

As it provides both versions, it provides a backwards-compatible API while allowing new code to utilize the const correct version.

The change to vtkObject was necessary to get the build to work; I made the `GetDebug' method const.


Would you accept more patches of this nature?
TagsNo tags attached.
Relationships
Attached Filespatch const.patch (1,627) 2008-06-14 17:43
https://www.vtk.org/Bug/file/6529/const.patch
Issue History
Date ModifiedUsernameFieldChange
2008-06-14 17:43Tom FogalNew Issue
2008-06-14 17:43Tom FogalFile Added: const.patch
2008-06-14 19:16Tom FogalNote Added: 0012344
2011-06-16 13:11Zack GalbreathCategory => (No Category)
2016-08-12 09:54Kitware RobotNote Added: 0036988
2016-08-12 09:54Kitware RobotStatusexpired => closed
2016-08-12 09:54Kitware RobotResolutionopen => moved
2016-08-12 09:54Kitware RobotAssigned To => Kitware Robot

Notes
(0012344)
Tom Fogal   
2008-06-14 19:16   
I was thinking that it might be better for constants to utilize references instead of pointers. This would differentiate their use -- since stack-based VTK objects are currently disallowed, it would call attention to the fact that whatever VTK object you have obtained via such a mechanism is constant.

More concretely, this would mean that as I read code such as:
   v = XYZ->GetFoo().GetBar().GetBaz();

I know that
   1) `XYZ' is a pointer; it is likely to be a mutable pointer.
   2) I don't know the return type of GetFoo, but I know that the `Foo' is RO.
   3) Likewise with `Bar', and `Baz'

(1) comes from the fact that if the VTK library provides const& methods but not many const* methods, then the programmer would have to `break convention' to obtain a constant pointer (e.g. call a mutable method that returns a pointer, but store it in a pointer to const). (2) and (3) are useful because they do not require me to go load up the vtk.org doxygen documentation.

Thoughts?
(0036988)
Kitware Robot   
2016-08-12 09:54   
Resolving issue as `moved`.

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