Add :== unapply to Chain. (#2996)

* Add :== unapply to Chain. * use 'init' and 'last'.
typelevel · Aug 20, 2019 · 48c8b34 · 48c8b34
1 parent a97bb9a
commit 48c8b34
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Showing 2 changed files with 11 additions and 1 deletion.
diff --git a/core/src/main/scala/cats/data/Chain.scala b/core/src/main/scala/cats/data/Chain.scala
@@ -541,6 +541,11 @@ object Chain extends ChainInstances {
       c.uncons
   }
 
+  object :== {
+    def unapply[T](c: Chain[T]): Option[(Chain[T], T)] =
+      c.initLast
+  }
+
   /** 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
@@ -3,6 +3,7 @@ package tests
 
 import cats.data.Chain
 import cats.data.Chain.==:
+import cats.data.Chain.`:==`
 import cats.laws.discipline.{
   AlternativeTests,
   CoflatMapTests,
@@ -75,7 +76,7 @@ class ChainSuite extends CatsSuite {
     }
   }
 
-  test("list-like pattern match") {
+  test("seq-like pattern match") {
     Chain(1, 2, 3) match {
       case Chain(a, b, c) => (a, b, c) should ===((1, 2, 3))
     }
@@ -84,6 +85,10 @@ class ChainSuite extends CatsSuite {
       case h ==: t => (h, t) should ===(1 -> Chain(2, 3))
     }
 
+    Chain(1, 2, 3) match {
+      case init :== last => (init, last) should ===(Chain(1, 2) -> 3)
+    }
+
   }
 
   test("size is consistent with toList.size") {