Below is a dialogue between software developers, the first one used ChatGPT in his solution of code task and makes a comment,   the second one gives him reply on his solution. Write a reply that appropriately answers the comment.

### Comment:
 related issue_no response_ googling result chatgpt result your question herein graph.rs, nodehandleadd_edge have self while subgraphadd_node have mut self.i believe both should be mut self, since both somehow modifies the struct.i thought maybe there is some contrived way like using rc or refcell or similar tools to bypass this restriction, and used chatgpt to find that, but to no success.it would be grateful to know whether this difference is intended or not.### Reply:
yes, its quite intended, and you found the point regarding mutability! keep going