HList_apply_Idx (#2967)

slick-testkit/src/test/scala/slick/test/collection/heterogeneous/HListTest.scala

@@ -3,16 +3,15 @@ package slick.test.collection.heterogeneous
 import org.junit.Test
 import org.junit.Assert._
 import slick.collection.heterogeneous.*
-import org.w3c.dom.Text
-
+import scala.util.*
 
 class HListTest {
 
   val hl1 = "test" :: HNil
   val hl2 = 1 :: "test2" :: HNil
 
   val c = hl1 ::: hl2
- val cc = c ::: c
+  val cc = c ::: c
 
   @Test
   def concatTest: Unit = {
@@ -49,4 +48,29 @@ class HListTest {
 
   }
 
+  @Test
+  def idx: Unit = {
+
+    assert(Try(HNil(0)).isFailure)
+
+    assert(hl1(0) == hl1.head)
+
+    assert(Try(hl1(-1)).isFailure)
+
+    assert(Try(hl1(1)).isFailure)
+
+    assert(hl2(0) == hl2.head)
+
+    assert(hl2(1) == hl2.tail.head)
+
+    assert(c(0) == c.head)
+
+    assert(c(1) == c.tail.head)
+
+    assert(c(2) == c.tail.tail.head)
+
+    assert(Try(c(3)).isFailure)     
+  }
+
+
 }

slick/src/main/scala/slick/collection/heterogeneous/HList.scala

@@ -44,6 +44,19 @@ sealed abstract class HList extends Product {
     i
   }
 
+  def apply(idx: Int): Any = {
+    require(idx >= 0, "Index should be non negative")
+    var i = 0
+    var h = this
+    while(h.nonEmpty && i < idx) {
+      i += 1
+      h = h.tail
+    }
+    if(i < idx) throw new IndexOutOfBoundsException 
+    h.head
+  } 
+
+
   /** Prepend an element to this HList, returning a new HList. */
   @inline final def :: [E](elem: E): :: [E] = new HCons[E, Self](elem, this.asInstanceOf[Self])