How can I make a structure with internal references?

Question

I\'m trying to make a graph with adjacency lists, but I can\'t figure out how to specify an appropriate lifetime for the references in the adjacency list.

What I\'m

Answer 1

I think there is an issue here. If we transpose this to C++:

template 
struct Graph {
    std::vector nodes;
    std::vector> adjacencies;
};

where adjacencies points into nodes, then one realizes that there is an issue: an operation on nodes that invalidates references (such as reallocation) will leave dangling pointers into adjacencies.

I see at least two ways to fix this:

• Use indexes in adjacencies, as those are stable
• Use a level of indirection in nodes, so that the memory is pinned

In Rust, this gives:

struct Graph {
    nodes: Vec,
    adjacencies: Vec>,
};

struct Graph {
    nodes: Vec>>,
    adjacencies: Vec>>>,
};

Note: the RefCell is to allow mutating T despite it being aliased, by introducing a runtime check.