The "trees" project written in rust aims at:

a fundamental library for storing and manipulating tree-like data structures.
expressing hierarchical data conveniently and compactly.

The implementation is straightforward:

none-intrusive nodes with child-sibling pointers.
children nodes, or forest, are singly-linked circular list.

This crate does not depend on libstd, and can be regarded as the nonlinear version of std::collections::LinkedList.

API document: docs.rs

Quick start

Tree notation

use trees::tr;      // tr stands for tree
tr(0);              // A single tree node with data 0. tr(0) has no children
tr(0) /tr(1);       // tr(0) has one child tr(1)
tr(0) /tr(1)/tr(2); // tr(0) has children tr(1) and tr(2)

// tr(0) has children tr(1) and tr(4), while tr(1) has children tr(2) and tr(3), and tr(4) has children tr(5) and tr(6).
// The spaces and carriage returns are for pretty format and do not make sense.
tr(0)
    /( tr(1) /tr(2)/tr(3) )
    /( tr(4) /tr(5)/tr(6) );

Forest notation

use trees::{tr,fr}; // fr stands for forest

fr::<i32>();        // An empty forest
fr() - tr(1);       // forest has one child tr(1)
- tr(1);            // forest has one child tr(1). The fr() can be omitted. The Neg operator for Tree converts the tree to a forest.
- tr(1) - tr(2);    // forest has child tr(1) and tr(2)
tr(1) - tr(2);      // forest has child tr(1) and tr(2). The leading neg can be omitted.

// forest has children tr(1) and tr(4), while tr(1) has children tr(2) and tr(3), and tr(4) has children tr(5) and tr(6).
-( tr(1) /tr(2)/tr(3) )
-( tr(4) /tr(5)/tr(6) );

// A tree tr(0) whose children equal to the forest descripted above.
tr(0) /(
    -( tr(1) /( -tr(2)-tr(3) ) )
    -( tr(4) /( -tr(5)-tr(6) ) )
);

Preorder traversal

use std::string::{String,ToString};
use trees::{tr,Node};

let tree = tr(0)
    /( tr(1) /tr(2)/tr(3) )
    /( tr(4) /tr(5)/tr(6) );

fn tree_to_string<T:ToString>( node: &Node<T> ) -> String {
    if node.is_leaf() {
        node.data.to_string()
    } else {
        node.data.to_string()
            + &"( "
            + &node.children()
                .fold( String::new(),
                    |s,c| s + &tree_to_string(c) + &" " )
            + &")"
    }
}

assert_eq!( tree_to_string( &tree ), "0( 1( 2 3 ) 4( 5 6 ) )" );

String representation

The Debug and Display trait has been implemented and are essentially the same as tree_to_tring() mentioned above.

Children are seperated by spaces and grouped in the parentheses that follow their parent closely.

use trees::{tr,fr};

let tree = tr(0) /( tr(1) /tr(2)/tr(3) ) /( tr(4) /tr(5)/tr(6) );
let str_repr = "0( 1( 2 3 ) 4( 5 6 ) )";
assert_eq!( tree.to_string(), str_repr );
assert_eq!( format!( "{:?}", tree ), str_repr );

assert_eq!( fr::<i32>().to_string(), "()" );
assert_eq!( format!( "{:?}", fr::<i32>() ), "()" );

let forest = -( tr(1) /tr(2)/tr(3) ) -( tr(4) /tr(5)/tr(6) );
let str_repr = "( 1( 2 3 ) 4( 5 6 ) )";
assert_eq!( forest.to_string(), str_repr );
assert_eq!( format!( "{:?}", forest ), str_repr );

Slow start

Concepts

Tree is composed of a root Node and an optional Forest as its children. A tree can NOT be empty.

use trees::{tr,Tree,Forest};

let tree: Tree<i32> = tr(0);
let forest: Forest<i32> = -tr(1)-tr(2)-tr(3);
let mut tree = tree.adopt( forest );
let forest = tree.abandon();

Forest is composed of Nodes as its children. A forest can be empty.

use trees::{tr,fr,Tree,Forest};

let mut forest: Forest<i32> = fr(); // an empty forest
forest.push_back( tr(1) );          // forest has one tree
forest.push_back( tr(2) );          // forest has two trees

Node is a borrowed tree, and Tree is an owned Node. All nodes in a tree can be referenced as &Node, but only the root node can be observed as Tree by the user.

use trees::{tr,Tree,Node};
use std::borrow::Borrow;

let mut tree: Tree<i32>  = tr(0) /tr(1)/tr(2)/tr(3);
{
    let root: &Node<i32> = tree.borrow();
    let first_child : &Node<i32> = tree.children().next().unwrap();
    let second_child: &Node<i32> = tree.children().nth(2).unwrap();
    let third_child : &Node<i32> = tree.children().last().unwrap();
}
let first_child: Tree<i32> = tree.pop_front().unwrap();

Iterators

The children nodes of a node, or a forest, is conceptually a forward list.

Using children() to iterate over referenced child Nodes, you can:
- read the data associated with each node.
- using children() to iterate over children's children, perhaps read the data associated with children's children, etc.
Using children_mut() to iterate over referenced child Nodes, you can:
- read/write the data associated with each node, or adopt(), abandon(), push_front(), pop_front(), push_back() child node(s) in constant time.
- using children_mut() to iterate over children's children, perhaps read/write the data associated with children's children, or adopt(), abandon(), push_front(), pop_front(), push_back() child node(s) in constant time, etc.
Using subtrees() to iterate over Subtrees, you can:
- insert_sib(), remove() node(s) at given position in the children forward list in O(n) time.
- do whatever children() or children_mut() allows to do.
Using Forest::<T>::into_iter() to iterate over Trees, you can:
- do whatever you want to.

Resource management

Tree/Forest are implemented in extrusive manner with two extra pointers per node, and will recursively destruct all the nodes owned by the tree/forest when reaching the end of their lifetimes.
Clone for Tree and Forest makes deep copy which clones all its decendant nodes. To do copy for just one node, simplely let cloned = trees::tr( node.data.clone() );.
No bookkeeping of size information.

Panics

No panics unless Clone is involved:

Node::<T>::to_owned()
Tree::<T>::clone()
Forest::<T>::clone()
all of the operator overloading functions the operands of which contain at least one referenced type.