Improving Observer Design Implementation for itk::Object.

Engineering
1

Hello, everyone. I work with ITK at my day job. Upon inspection into the header of itkObject, I noticed there is a const API available for AddObserver but not for RemoveObserver. Since both APIs internally just call the mutable m_SubjectImplementation’s RemoveObserver(), would it make sense to provide a const version of the RemoveObserver API just like AddObserver()?
Here’s a patch, if you’d like to accept the proposal:-

index 3a63ffaa45..f2ba3d7dd5 100644
--- a/Modules/Core/Common/src/itkObject.cxx
+++ b/Modules/Core/Common/src/itkObject.cxx
@@ -494,6 +494,13 @@ Object::GetCommand(unsigned long tag)
void
Object::RemoveObserver(unsigned long tag)
+{
+  const auto & thisAsConst = *this;
+  return thisAsConst.RemoveObserver(tag);
+}
+
+void
+Object::RemoveObserver(unsigned long tag) const
{
if (this->m_SubjectImplementation)
{
    this->m_SubjectImplementation->RemoveObserver(tag);
  }
}
2

Here’s the link to RemoveObserver() API on GitHub:
ITK/Modules/Core/Common/src/itkObject.cxx at master · InsightSoftwareConsortium/ITK · GitHub

3

PR xref: