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This post is auto-generated from RSS feed The Rust Programming Language Forum - Latest topics. Source: Recursive lifetime issue: child holding a reference to a parent of the same type

Hi!
I need to have a tree-like data structure, where every node is the same type, and where each child references it's parent. I tried different things, and eventually found one working, but I can't tell why it's working.
Some minimal example code is here in the playground.

In short, I want somthing like:

pub enum Tree<'parent> {
    Root,
    Child(&'parent Tree<'idk-what-to-put-here>),
}

Of course, this code doesn't work.

The solution I found (in the playground) is really weird:

enum Tree<'parent, 'grandparent> {
    Root,
    Child(&'parent Tree<'grandparent, 'parent>),
}

In the 0 field of Child, the 'grandparent and 'parent lifetimes are... inverted? compared to the order of the arguments in the struct. It's weird.

The closest post I found about this problem is this one, but I couldn't find a satisfactory answer here.

Can someone give me an explanation to this? And eventually a better solution?

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