CollectionItemElementSelector now returns a constant hashCode

The ElementSelector `hashCode` is only needed to use it as key in a
Map. With introduction of the `IdentityStrategy` this adds an
unnecessary source of confusion and complexity when implementing custom
IdentityStrategies.

To avoid this, returning a constant hashCode seems like a small price
to pay. Yes, it may have a small performance impact, but we can still
optimize when that turns out to be a problem.

Author: SQiShER

CHANGELOG.md

@@ -1,5 +1,20 @@
 # Changelog
 
+## 0.92.2
+
+- **ElementSelector:** `CollectionItemElementSelector` now returns a constant hashCode
+
+	...instead of the one of its reference item.
+
+	The ElementSelector `hashCode` is only needed to use it as key in a 
+    Map. With introduction of the `IdentityStrategy` this adds an 
+    unnecessary source of confusion and complexity when implementing custom
+    IdentityStrategies. 
+    
+    To avoid this, returning a constant hashCode seems like a small price
+    to pay. Yes, it may have a small performance impact, but we can still
+    optimize when that turns out to be a problem.
+
 ## 0.92.1
 
 - **Feature:** Allow for checking field level annotations via DiffNode (Thanks [@NagyGa1](https://github.com/NagyGa1)) [#134]

src/main/java/de/danielbechler/diff/selector/CollectionItemElementSelector.java

@@ -71,6 +71,6 @@ public boolean equals(final Object o)
 	@Override
 	public int hashCode()
 	{
-		return item != null ? item.hashCode() : 0;
+		return 31;
 	}
 }

src/test/java/de/danielbechler/diff/selector/CollectionItemElementSelectorTest.groovy

@@ -1,7 +1,6 @@
 package de.danielbechler.diff.selector
 
 import spock.lang.Specification
-
 /**
  * @author Daniel Bechler
  */
@@ -37,13 +36,16 @@ class CollectionItemElementSelectorTest extends Specification {
 		  !element.equals(null)
 	}
 
-	def 'should have same hashCode as item'() {
-		setup:
-		  def item = "foo"
-		  def element = new CollectionItemElementSelector(item)
+	def 'should have constant hashCode'() {
+		// NOTE(@SQiShER): In this case the hashCode is only used to use the ElementSelector
+		// as key in a Map. With introduction of the IdentityStrategy this adds an unnecessary
+		// source of confusion and complexity when implementing custom IdentityStrategies. To
+		// avoid this, returning a constant hashCode seems like a small fee to pay. Yes, it may
+		// have a small performance impact, but we can still optimize when it turns out to
+		// actually be a problem.
 
 		expect:
-		  element.hashCode() == item.hashCode()
+		  new CollectionItemElementSelector('foo').hashCode() == 31
 	}
 
 	def 'should provide accessor for item'() {