#多相な関数の定義から学ぶ、型クラスデザインパターン
twitter: @OE_uia github: taisukeoe
##多相な関数
- 複数の異なる型に対して適用可能な関数
- どの型に対して定義されているか、静的に決定できる(定義されてない型の値を渡すとコンパイルエラーになる)
| 01-13 02:59:43.556 21402-21402/com.example.android.displayingbitmaps E/AndroidRuntime: FATAL EXCEPTION: main | |
| 01-13 02:59:43.556 21402-21402/com.example.android.displayingbitmaps E/AndroidRuntime: Process: com.example.android.displayingbitmaps, PID: 21402 | |
| 01-13 02:59:43.556 21402-21402/com.example.android.displayingbitmaps E/AndroidRuntime: java.lang.NoClassDefFoundError: Failed resolution of: Ljavax/imageio/ImageIO; | |
| 01-13 02:59:43.556 21402-21402/com.example.android.displayingbitmaps E/AndroidRuntime: at org.canova.image.recordreader.BaseImageRecordReader.<clinit>(BaseImageRecordReader.java:72) | |
| 01-13 02:59:43.556 21402-21402/com.example.android.displayingbitmaps E/AndroidRuntime: at com.example.android.displayingbitmaps.ui.ImageGridActivity.trainMLP(ImageGridActivity.java:99) | |
| 01-13 02:59:43.556 21402-21402/com.example.android.displayingbitmaps E/AndroidRuntime: at com.example.android.displayingbitmaps.ui.ImageGridActivity.onCreate(ImageGridActivity.java:72) | |
| 01-13 02:59:43.556 21402-21402/com.examp |
| ```scala | |
| implicit def cofreeEqual[A, F[_]](implicit A: Equal[A], F: Equal[F[Cofree[F, A]]]): Equal[Cofree[F, A]] = | |
| Equal.equal{ (a, b) => | |
| A.equal(a.head, b.head) && F.equal(a.tail, b.tail) | |
| } | |
| scala> import scalaz._,Scalaz._ | |
| import scalaz._ | |
| import Scalaz._ |
| Welcome to Scala 2.12.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_201). | |
| Type in expressions for evaluation. Or try :help. | |
| scala> trait A {val x:AnyRef = null;type X = x.type} | |
| defined trait A | |
| scala> val a = new A{} | |
| a: A = $anon$1@36417a54 | |
| scala> val ax:a.type#X = a.x |
| import cats._ | |
| import cats.data.{Kleisli, Reader, ReaderT} | |
| import cats.implicits._ | |
| import scala.concurrent.{ExecutionContext, Future} | |
| object ReaderStyle extends App { | |
| def someCalc(i: Int): Int = ??? | |
| import ExecutionContext.Implicits.global |
| import cats. | |
| import cats.implicits._ | |
| case class MyError(errorMsg: String) | |
| object MyError { | |
| implicit val s: Semigroup[MyError] = new cats.kernel.Semigroup[MyError] { | |
| override def combine(t1: MyError, t2: MyError): MyError = MyError(t1.errorMsg + "\n" + t2.errorMsg) | |
| } | |
| } |