Count even() and odd() from zero, as jQuery and :even/:odd do

CHANGELOG.md

@@ -58,6 +58,7 @@ QueryPath Changelog
 - Consolidate the sibling and ancestor walks behind `next()`, `prev()`, `nextAll()`, `prevAll()`, `nextUntil()`, `prevUntil()`, `parent()`, `parents()`, `parentsUntil()` and `closest()` into one helper, so a fix to one no longer has to be repeated in its mirror (issue #115). As a side effect, `parentsUntil()` no longer loops forever on an element that is not attached to the document, and `nextUntil('')` and `prevUntil('')` treat an empty selector as no selector, as the other methods already did, instead of throwing `QueryPath\CSS\ParseException`. `closest('')` returns an empty set, as in jQuery. `nextUntil()`, `prevUntil()` and `parentsUntil()` also stop at an element already collected from an earlier starting element, as `nextAll()` and `prevAll()` do, so `nextUntil()` on each of 2000 siblings falls from about 100 ms to 1 ms
 - **Behaviour change.** `prevAll()`, `prevUntil()`, `nextAll()`, `nextUntil()`, `siblings()`, `parent()` and `closest()` now return the results for a multi-element set in jQuery's order, instead of grouped by starting element (issue #117). `prevAll()` and `prevUntil()` return reverse document order, as `parents()` and `parentsUntil()` already did, and the others return document order. `qp($xml, 'c')->add('d')->prevAll()` now returns `c, b, a` rather than `b, a, c`. `next()` and `prev()` keep the order of the starting elements, as in jQuery, and the results for a single starting element are unchanged
 - **Behaviour change.** A positional pseudo-class (`:first`, `:eq()`, `:last`, ...) in the stop selector of `nextUntil()`, `prevUntil()` and `parentsUntil()` now counts across the whole document, as jQuery's does, instead of seeing each sibling or ancestor as a one-element set (issue #118). `nextUntil(':first')` used to stop at once and now walks to the end, and `nextUntil(':eq(3)')` stops at the fourth element in the document. `closest()` no longer matches a positional selector at all, as in jQuery, where `closest(':first')` used to return the element itself. `next()`, `prev()` and `parent()` still test each candidate on its own, which agrees with jQuery for a single starting element
+- **Breaking behaviour change.** `even()` and `odd()` now count from zero, as jQuery's `.even()` and `.odd()` and QueryPath's own `:even` and `:odd` pseudo-classes do (issue #145). `even()` keeps the 1st, 3rd, 5th, ... matches and `odd()` keeps the 2nd, 4th, ..., the reverse of before. Swap the calls to keep the previous result
 
 # 4.2.0
 

src/Helpers/QueryFilters.php

@@ -373,56 +373,52 @@ public function eachLambda($lambda): Query
 	}
 
 	/**
-	 * Get the even elements, so counter-intuitively 1, 3, 5, etc.
+	 * Get the matches at zero-based even positions (0, 2, 4, ...), as jQuery's .even() and
+	 * the :even pseudo-class do.
 	 *
 	 * @return DOMQuery
-	 *  A DOMQuery wrapping all of the children.
+	 *  A DOMQuery wrapping the matches at even positions.
 	 * @throws ParseException
-	 * @see    parent()
-	 * @see    parents()
-	 * @see    next()
-	 * @see    prev()
+	 * @see    odd()
 	 * @since  2.1
 	 * @author eabrand
-	 * @see    removeChildren()
 	 */
 	public function even(): Query
 	{
-		$found = new SplObjectStorage();
-		$even  = false;
-		foreach ($this->matches as $m) {
-			if ($even && $m->nodeType === XML_ELEMENT_NODE) {
-				$found->offsetSet($m);
-			}
-			$even = $even ? false : true;
-		}
-
-		return $this->inst($found, null);
+		return $this->positional('even');
 	}
 
 	/**
-	 * Get the odd elements, so counter-intuitively 0, 2, 4, etc.
+	 * Get the matches at zero-based odd positions (1, 3, 5, ...), as jQuery's .odd() and
+	 * the :odd pseudo-class do.
 	 *
 	 * @return DOMQuery
-	 *  A DOMQuery wrapping all of the children.
+	 *  A DOMQuery wrapping the matches at odd positions.
 	 * @throws ParseException
-	 * @see    parent()
-	 * @see    parents()
-	 * @see    next()
-	 * @see    prev()
+	 * @see    even()
 	 * @since  2.1
 	 * @author eabrand
-	 * @see    removeChildren()
 	 */
 	public function odd(): Query
+	{
+		return $this->positional('odd');
+	}
+
+	/**
+	 * Apply a positional pseudo-class (`even`, `odd`, ...) to the match set, as filter() would.
+	 *
+	 * @param string $name
+	 *
+	 * @return DOMQuery
+	 * @throws ParseException
+	 */
+	private function positional(string $name): Query
 	{
 		$found = new SplObjectStorage();
-		$odd   = true;
-		foreach ($this->matches as $m) {
-			if ($odd && $m->nodeType === XML_ELEMENT_NODE) {
+		foreach (Util::applyPositionalPseudoClass(iterator_to_array($this->matches, false), $name) as $m) {
+			if ($m->nodeType === XML_ELEMENT_NODE) {
 				$found->offsetSet($m);
 			}
-			$odd = $odd ? false : true;
 		}
 
 		return $this->inst($found, null);

tests/Issues/Issue145Test.php

@@ -0,0 +1,38 @@
+<?php
+/**
+ * @file
+ *
+ * Regression tests for https://github.com/GravityPDF/querypath/issues/145
+ *
+ * even() and odd() count from zero, as jQuery and the :even/:odd pseudo-classes do.
+ * Expected values are jQuery 3.7.1's.
+ */
+
+namespace QueryPathTests;
+
+class Issue145Test extends TestCase
+{
+	private const XML = '<?xml version="1.0"?><r><i id="a"/><i id="b"/><i id="c"/><i id="d"/><i id="e"/></r>';
+
+	public function testEvenKeepsTheZeroBasedEvenPositions()
+	{
+		$this->assertSame('a,c,e', $this->idList(qp(self::XML, 'i')->even()));
+		$this->assertSame('a', $this->idList(qp(self::XML, '#a')->even()));
+		$this->assertSame('', $this->idList(qp(self::XML, 'nothing')->even()));
+	}
+
+	public function testOddKeepsTheZeroBasedOddPositions()
+	{
+		$this->assertSame('b,d', $this->idList(qp(self::XML, 'i')->odd()));
+		$this->assertSame('', $this->idList(qp(self::XML, '#a')->odd()));
+		$this->assertSame('', $this->idList(qp(self::XML, 'nothing')->odd()));
+	}
+
+	public function testEvenAndOddAgreeWithThePseudoClasses()
+	{
+		$qp = qp(self::XML, 'i');
+
+		$this->assertSame($this->idList($qp->filter(':even')), $this->idList($qp->even()));
+		$this->assertSame($this->idList($qp->filter(':odd')), $this->idList($qp->odd()));
+	}
+}

tests/QueryPath/DOMQueryTest.php

@@ -2460,14 +2460,14 @@ public function testEven()
 	{
 		$file = DATA_FILE;
 		$this->assertEquals(1, qp($file, 'inner')->even()->count());
-		$this->assertEquals(2, qp($file, 'li')->even()->count());
+		$this->assertEquals(3, qp($file, 'li')->even()->count());
 	}
 
 	public function testOdd()
 	{
 		$file = DATA_FILE;
 		$this->assertEquals(1, qp($file, 'inner')->odd()->count());
-		$this->assertEquals(3, qp($file, 'li')->odd()->count());
+		$this->assertEquals(2, qp($file, 'li')->odd()->count());
 	}
 
 	public function testFirst()