constify AlignmentHandle::operator[]

git-svn-id: https://dng.biozentrum.unibas.ch/svn/openstructure/trunk@2024 5a81b35b-ba03-0410-adc8-b2c5c5119f08

modules/seq/base/src/alignment_handle.cc

@@ -226,7 +226,7 @@ AlignedColumnIterator AlignmentHandle::end() const
   return AlignedColumnIterator(*this, this->GetLength(), this->GetLength());
 }
 
-AlignedColumn AlignmentHandle::operator[](int index)
+AlignedColumn AlignmentHandle::operator[](int index) const
 {
   return AlignedColumn(*this, index);
 }

modules/seq/base/src/alignment_handle.hh

@@ -135,7 +135,7 @@ public:
   /// This method does not throw any exception. Upon accessing methods of the 
   /// aligned column, exceptions might be thrown when the index is out of 
   /// bounds.
-  AlignedColumn operator[](int index);
+  AlignedColumn operator[](int index) const;
   
   AlignmentHandle(const impl::SequenceListImplPtr& impl);