const after initialization / pointers, references and values

[Vicente via Digitalmars-d]

Indeed the ref can be applied to the return type:
http://dlang.org/function.html#ref-functions

So, does the following code copy any data from "nodes"?
If that is the case this solution avoids the "class" storage, 
avoids pointers and "nodes" is encapsulated as read-only, that's 
great.
The program I'm working on is still incomplete, so I still can't 
benchmark it to compare with all proposed solutions.

@safe:
import std.stdio;
import std.string;

struct Node {
	Node[] block;
	uint num = 0;
};

immutable uint LAST = -1;
Node[] default_nodes = [
	{num:3},
	{block:[{num:4},{num:6},{block:[{num:5},{num:7}]}]},
	// ...
	{num:LAST},
];

class NodeProvider{
	// change to const after constructor
	private Node[] nodes;

	private void parse_file(char[] file_name){
		// initialize nodes from file
		for(auto i=0; i<3; i++){
			nodes.length++;
			nodes[$-1].num=i;
		}
		nodes.length++;
		nodes[$-1].num=LAST;
	}

	this(){
		nodes = default_nodes;
	}
	this(char[] file_name){
		parse_file(file_name);
	}

	ref const(Node) get_node(const uint index){
		return nodes[index];
	}
}

string NodetoString(ref const(Node) n){
	string str = format("%u{ ", n.num);
	foreach(b;n.block)
		str ~= NodetoString(b);
	str ~= "} ";
	return str;
}

@system: // for writeln
int main(char[][] args){
	NodeProvider np;
	uint i;

	if(args.length==2)
		np = new NodeProvider(args[1]);
	else
		np = new NodeProvider();

	for(i=0;;i++){
		const(Node) node = np.get_node(i);
		if(node.num==LAST)
			break;
		writeln(NodetoString(node));
	}
	return 0;
}