Merge pull request #1454 from edmundnoble/eitheridops

Either .left, .right syntax
typelevel · Nov 7, 2016 · 9af39fb · 9af39fb
2 parents 2fd55c5 + 2538b0e
commit 9af39fb
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diff --git a/core/src/main/scala/cats/syntax/either.scala b/core/src/main/scala/cats/syntax/either.scala
@@ -13,6 +13,8 @@ trait EitherSyntax {
   implicit def catsSyntaxLeft[A, B](left: Left[A, B]): LeftOps[A, B] = new LeftOps(left)
 
   implicit def catsSyntaxRight[A, B](right: Right[A, B]): RightOps[A, B] = new RightOps(right)
+
+  implicit def catsSyntaxEitherId[A](a: A): EitherIdOps[A] = new EitherIdOps(a)
 }
 
 final class EitherOps[A, B](val eab: Either[A, B]) extends AnyVal {
@@ -306,6 +308,14 @@ final class RightOps[A, B](val right: Right[A, B]) extends AnyVal {
   def leftCast[C]: Either[C, B] = right.asInstanceOf[Either[C, B]]
 }
 
+final class EitherIdOps[A](val obj: A) extends AnyVal {
+  /** Wrap a value in `Left`. */
+  def asLeft[B]: Either[A, B] = Left(obj)
+
+  /** Wrap a value in `Right`. */
+  def asRight[B]: Either[B, A] = Right(obj)
+}
+
 /** Convenience methods to use `Either` syntax inside `Either` syntax definitions. */
 private[cats] object EitherUtil {
   def leftCast[A, B, C](right: Right[A, B]): Either[C, B] =

diff --git a/tests/src/test/scala/cats/tests/EitherTests.scala b/tests/src/test/scala/cats/tests/EitherTests.scala
@@ -57,6 +57,13 @@ class EitherTests extends CatsSuite {
     }
   }
 
+  test("Left/Right id syntax") {
+    forAll { (e: Int) =>
+      assert(Left[Int, String](e) === e.asLeft[String])
+      assert(Right[String, Int](e) === e.asRight[String])
+    }
+  }
+
   test("implicit instances resolve specifically") {
     val eq = catsStdEqForEither[Int, String]
     assert(!eq.isInstanceOf[PartialOrder[_]])