From e1c5e77be6a795dc2d02f59d298642e776563546 Mon Sep 17 00:00:00 2001
From: Bondarenko <vasiliy.bondarenko@gmail.com>
Date: Thu, 15 Aug 2019 13:44:04 +0300
Subject: [PATCH] unapplySeq in Chain (issue #2960)

---
 core/src/main/scala/cats/data/Chain.scala        |  8 ++++++++
 tests/src/test/scala/cats/tests/ChainSuite.scala | 12 ++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/core/src/main/scala/cats/data/Chain.scala b/core/src/main/scala/cats/data/Chain.scala
index 03b0a2aaa7..a09d27c526 100644
--- a/core/src/main/scala/cats/data/Chain.scala
+++ b/core/src/main/scala/cats/data/Chain.scala
@@ -531,6 +531,14 @@ object Chain extends ChainInstances {
       false // b/c `fromSeq` constructor doesn't allow either branch to be empty
   }
 
+  def unapplySeq[A](chain: Chain[A]): Option[Seq[A]] =
+    Some(chain.toList)
+
+  object ==: {
+    def unapply[T](c: Chain[T]): Option[(T, Chain[T])] =
+      c.uncons
+  }
+
   /** Empty Chain. */
   val nil: Chain[Nothing] = Empty
 
diff --git a/tests/src/test/scala/cats/tests/ChainSuite.scala b/tests/src/test/scala/cats/tests/ChainSuite.scala
index 042a8a86c3..ca22f17003 100644
--- a/tests/src/test/scala/cats/tests/ChainSuite.scala
+++ b/tests/src/test/scala/cats/tests/ChainSuite.scala
@@ -2,6 +2,7 @@ package cats
 package tests
 
 import cats.data.Chain
+import cats.data.Chain.==:
 import cats.laws.discipline.{
   AlternativeTests,
   CoflatMapTests,
@@ -74,6 +75,17 @@ class ChainSuite extends CatsSuite {
     }
   }
 
+  test("list-like pattern match") {
+    Chain(1, 2, 3) match {
+      case Chain(a, b, c) => (a, b, c) should ===((1, 2, 3))
+    }
+
+    Chain(1, 2, 3) match {
+      case h ==: t => (h, t) should ===(1 -> Chain(2, 3))
+    }
+
+  }
+
   test("size is consistent with toList.size") {
     forAll { (ci: Chain[Int]) =>
       ci.size.toInt should ===(ci.toList.size)