Macro tree

tree!() { /* proc-macro */ }

Construct a tree for a given arena.

This macro creates a tree in an Arena with a pre-defined layout. If the root node is of type NodeId, then that NodeId is used for the root node, but if it’s any other type, then it creates a new root node on-the-fly. The macro returns NodeId of the root node.

Examples

let root_node = arena.new_node("root node");
tree!(
    &mut arena,
    root_node => {
        "1",
        "2" => {
            "2_1" => { "2_1_1" },
            "2_2",
        },
        "3",
    }
);

let automagical_root_node = tree!(
    &mut arena,
    "root node, but automagically created" => {
        "1",
        "2" => {
            "2_1" => { "2_1_1" },
            "2_2",
        },
        "3",
    }
);

Note that you can anchor the root node in the macro to any node at any nesting. So you can take an already existing node of a tree and attach another tree to it:

let root_node = tree!(
    &mut arena,
    "root node" => {
        "1",
        "2",
        "3",
    }
);

let node_1 = arena.get(root_node).unwrap().first_child().unwrap();
let node_2 = arena.get(node_1).unwrap().next_sibling().unwrap();
tree!(
    &mut arena,
    node_2 => {
        "2_1" => { "2_1_1" },
        "2_2",
    }
);

It is also possible to create an empty root_node, although, I’m not sure why you’d want to do that.

let root_node = tree!(
    &mut arena,
    "my root node",
);

Empty nodes can also be defined as => {}

let root_node = tree!(
    &mut arena,
    "my root node" => {},
);