User iterator rather than vector in matcher

Author: glyn

src/matchers.rs

@@ -5,19 +5,18 @@
  */
 
 use serde_json::Value;
+use std::iter::once;
 
 // Matcher maps a node to a list of nodes. If the input node is not matched by the matcher or
 // the matcher does not select any subnodes of the input node, then the result is empty.
 pub trait Matcher {
-    fn select<'a>(&self, node: &'a Value) -> Vec<&'a Value>;
+    fn select<'a>(&self, node: &'a Value) -> Box<dyn Iterator<Item = &'a Value> + 'a>;
 }
 
 pub struct RootSelector {}
 
 impl Matcher for RootSelector {
-    fn select<'a>(&self, node: &'a Value) -> Vec<&'a Value> {
-        let mut results = Vec::new();
-        results.push(node);
-        results
+    fn select<'a>(&self, node: &'a Value) -> Box<dyn Iterator<Item = &'a Value> + 'a> {
+        Box::new(once(node))
     }
 }

src/path.rs

@@ -28,14 +28,8 @@ impl Path for SelectorPath<'_> {
         // pass nodes, starting with document alone, through each matcher in turn
         Ok((&self.matchers)
             .iter()
-            .fold(doc_node(document), |nodes, matcher| {
+            .fold(vec![document], |nodes, matcher| {
                 nodes.iter().flat_map(|node| matcher.select(node)).collect()
             }))
     }
 }
-
-fn doc_node<'a>(document: &'a Value) -> Vec<&'a Value> {
-    let mut nodes = Vec::new();
-    nodes.push(document);
-    nodes
-}