All things considered, our experience in Scala Native has shown that resource management in Scala is way harder than it should be. This gist presents a simple design pattern that makes it resource management absolutely hassle-free: scoped implicit lifetimes.
The main idea behind it is to encode resource lifetimes through a concept of an implicit scope. Scopes are necessary to acquire resources. They are responsible for disposal of the resources once the evaluation exits the
| Welcome to Scala 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_45). | |
| Type in expressions for evaluation. Or try :help. | |
| scala> import scala.concurrent.ExecutionContext.Implicits.global | |
| import scala.concurrent.ExecutionContext.Implicits.global | |
| scala> scala.concurrent.Future( { println("foo"); 4 }) | |
| foo | |
| res0: scala.concurrent.Future[Int] = Success(4) |
| abstract class ExtFn(m: AnyRef) { | |
| type Out[A] | |
| def apply: Out[m.type] | |
| } |
| import scalaz.Monoid | |
| import scalaz.syntax.monoid._ | |
| import scalaz.syntax.traverse._ | |
| import scalaz.std.map._ | |
| import scalaz.std.anyVal._ | |
| import scalaz.std.string._ | |
| import scalaz.std.iterable._ | |
| import scala.language.higherKinds | |
| /* | |
| /* A Bounded Semi-lattice is a Monoid that is commutative and idempotent */ |
| object Main { | |
| val s1 = Set[BigDecimal](-4.872401723124452E9, 0, 1.1752011936438014, 8.696374707602505E17, -1.1752011936438014) | |
| val s2 = Set[Double] (-4.872401723124452E9, 0, 1.1752011936438014, 8.696374707602505E17, -1.1752011936438014) | |
| val s3: Set[BigDecimal] = s2 map (d => BigDecimal(d)) | |
| def main(args: Array[String]): Unit = { | |
| /* false */ println(s1 == s2) | |
| /* true */ println(s1 == s3) | |
| /* false */ println(s2 == s3) | |
| /* true */ println(s1.toSeq.sorted == s2.toSeq.sorted) |
| import shapeless.{HList, HNil, ::} | |
| import shapeless.ops.hlist.{Selector, Prepend} | |
| import shapeless.test.illTyped | |
| object TypeLevelBacktrack extends App { | |
| /** [[Parent]] / [[Child]] relationship, father side. */ | |
| trait FatherOf[Parent, Child] | |
| /** [[Parent]] / [[Child]] relationship, mother side */ | |
| trait MotherOf[Parent, Child] |
| data:text/html, <html contenteditable style="font-family:Courier New, Sans Serif;font-size:90px"> |
| scala> class Foo { self: Singleton => } | |
| defined class Foo | |
| scala> class Bar extends Foo | |
| <console>:12: error: illegal inheritance; | |
| self-type Bar does not conform to Foo's selftype Foo with Singleton | |
| class Bar extends Foo | |
| ^ | |
| scala> object Bar extends Foo |
| Symbol | Explanation | Hint |
|---|---|---|
\/ |
Right-leaning Either | Split ways, go one way or the other |
-\/ |
Left value of \/ |
- is on the left side |
\/- |
Right value of \/ |
- is on the right side |
>>= |
flatMap |
shove result into |
>> |
flatMap(_ => ..) |
shove into, but ignore the result |
|@| |
Applicatives into Tuple | Scream operator |
|+| |
Append via Monoid | + was taken |
| `> | ` | fa.map(_ => b) |
| import cats._, data._ | |
| object Test { | |
| trait Decoder[T] { | |
| def decode(s: String): String Xor T | |
| } | |
| case class Password(pw: String) | |
| case class User(name: String) |
