Scala implicit for mere mortals (like me)

One of the most difficult feature to master in Scala (at least for mere mortals of course) is the implicit keyword and its implications especially because it may appear in different places and for different purposes:

  • Implicit methods
  • Implicit parameters
  • Implicit variables
  • Implicit classes
  • Implicit constructors

So what is it useful for?
Implicits are essentially a way to leverage the power of Scala compiler by avoiding (otherwise) explicit calls to methods in our code or allowing us to extend native or third party classes “dynamically”.

Implicit methods

Implicits are used by Scala itself, for example: have you ever wonder why:

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val value: Double = 1 // <- this is an Int not a Double!

compiles without any issue and returns the expected value (1.0)? Implicit in action!
If we look at scala.Int companion object we will find the following implicit method declaration:

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implicit def int2double(x: Int): Double = x.toDouble

So, at compile-time, once the compiler finds a type mismatch in the code that will generate an exception (in this case an Int instead of a Double), it will check for an implicit in the current scope that is able to convert the wrong type into the correct one. If found, the compiler will replace the code by invoking the method for us:

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val value: Double = int2double(1) // <- explicit replacement

Let’s try to do a similar magic by ourselves. Let’s make the compiler be able to understand booleans as 'yes or 'no symbols:

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object MyApp {
  implicit def symbolToBoolean(symbol: Symbol): Boolean = {
    symbol match {
      case 'yes => true
      case 'no => false
    }
  }
  def main(args: Array[String]): Unit = {
    val scalaIsCool: Boolean = 'yes
    val scalaIsEasy: Boolean = 'no
    println(s"scalaIsCool: $scalaIsCool")
    println(s"scalaIsEasy: $scalaIsEasy")
  }
}

So, once the compiler encounters the following assignment:

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val scalaIsCool: Boolean = 'yes

Since a boolean can be only true or false, it will check for a way to give this symbol a boolean value, so it proceeds by checking the current scope (main() method), here there are no implicit definitions, so it goes up to the parent scope (MyApp), here it finds an implicit that is able to convert the symbol, so it will replace the code with:

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val scalaIsCool: Boolean = symbolToBoolean('yes)

and the same for the next line.
Of course this is just a dumb example and in the real life implicits are usually defined in separated classes.
We could rewrite the example as:

SymbolImplicits.scala

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object SymbolImplicits {
  implicit def symbolToBoolean(symbol: Symbol): Boolean = {
    symbol match {
      case 'yes => true
      case 'no => false
    }
  }
}

AppImportingImplicitMethods.scala

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import SymbolImplicits._
object MyApp {
  def main(args: Array[String]): Unit = {
    val scalaIsCool: Boolean = 'yes
    val scalaIsEasy: Boolean = 'no
    println(s"scalaIsCool: $scalaIsCool")
    println(s"scalaIsEasy: $scalaIsEasy")
  }
}

Implicit classes

One of the best use case for Scala implicit is to extend native or third party classes. Let’s pretend for example that we need to turn an arbitrary String into a slug, we could create an object like StringUtils with a method slufigy(string: String) but wouldn’t be much more clean to be able to call .toSlug against a String instance as we usually do with .toUpperCase and so on? Of course, and by defining an implicit class we can have such convenience:

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object StringExtensions {
  implicit class StringWrapper(string: String) {
    def toSlug: String = {
      string
        .toLowerCase
        .replaceAll("[^a-z\\d]", " ")
        .trim
        .replaceAll("\\s+", "-")
    }
  }
}

Then later on we can:

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import StringExtensions._
object MyApp {
  def main(args: Array[String]): Unit = {
    println(">> This string will be slugified! <<".toSlug)
  }
}

Bear in mind that an implicit class cannot be defined as a top-level object, therefore it must be “wrapped” by an object!

Implicit parameters

Also method parameters can be defined as implicit thus providing a sort of “native dependency injection”.
Let’s create a sample class which is responsible of creating a folder tree by naming folders according to the current date (/yyyy/MM/dd/):

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object FoldersCreator {
  def createDateFolderTree(root: Path)(implicit now: LocalDateTime): Option[Path] = {
    val format = (p: String) => now.format(DateTimeFormatter.ofPattern(p))
    val path: Path = Paths.get(root.toString, format("yyyy"), format("MM"), format("dd"))
    val result: Option[Path] = Try(Files.createDirectories(path)).toOption
    result
  }
  def createDateFolderTree(root: String)(implicit now: LocalDateTime): Option[Path] = {
    createDateFolderTree(Paths.get(root))
  }
}

As you can see I defined a method with an overload and both have a secondary couple of parenthesis containing a parameter now declared as implicit. This means that we will be able to call the methods without the second argument:

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FoldersCreator.createDateFolderTree("a/root/path")

Implicit variables

…provided that in the scope in which they get invoked an implicit variable of type LocalDateTime is found (the name doesn’t matter!).
Moreover as you can see even in the inner call from the overloaded method (createDateFolderTree(rootPath: String)...) to the original signature (createDateFolderTree(rootPath: Path)...) the second argument is omitted.
Let’s see how we can use the previously created object with implicit arguments:

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object MyApp {
  def main(args: Array[String]): Unit = {
    implicit val now: LocalDateTime = LocalDateTime.now()
    FoldersCreator.createDateFolderTree("/home/dave/Desktop")
    FoldersCreator.createDateFolderTree("/home/dave/Desktop/backup")
  }
}

In the code above the implicit variable has been defined just before invoking methods and it has been named like the argument in the signature (now).
However the implicit date can be declared also as class field and with a different name:

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object MyApp {
  private implicit val d: LocalDateTime = LocalDateTime.now()
  def main(args: Array[String]): Unit = {
    FoldersCreator.createDateFolderTree("/home/dave/Desktop")
    FoldersCreator.createDateFolderTree("/home/dave/Desktop/backup")
  }
}

If we define several implicit val, we may face a resolution exception. For example if we add a new implicit val of the same type (LocalDateTime) to the previous code:

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object MyApp {
  private implicit val date: LocalDateTime = LocalDateTime.now()
  private implicit val now: LocalDateTime = LocalDateTime.of(2020, 1, 1, 20, 30)
  def main(args: Array[String]): Unit = {
    FoldersCreator.createDateFolderTree("/home/dave/Desktop")
    FoldersCreator.createDateFolderTree("/home/dave/Desktop/backup")
  }
}

We will get:

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Error:(11, 40) ambiguous implicit values:
 both value date in object AppWithImplicitsVariables of type => java.time.LocalDateTime
 and value now in object AppWithImplicitsVariables of type => java.time.LocalDateTime
 match expected type java.time.LocalDateTime

This is a further proof that variable names don’t matter, only type does and if two variables with the same type are found in the scope the compiler doesn’t know which one to pick up.
Obviously in this case the problem is immediately spottable, but in a real application it might be harder to discover where is the conflict, especially if there are many classes with many implicits, generics and so on.

Implicit constructors

Like methods even constructor can be composed by implicit arguments.

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// an "injectable" object
class Bar
// a class with the implicit
class Foo(implicit val bar: Bar)
// tests app
object FooBarApp {
  private implicit val bar: Bar = new Bar
  def main(args: Array[String]): Unit = {
    val foo: Foo = new Foo
    println(foo.bar.getClass.getName)
  }
}

Final thoughts

The examples that I provided in this post are intentionally dumb and short, however with Scala implicit is possible to achieve complex tasks and automatically data conversion. For example Spark use this feature quite heavily for data encoding. Anyway this powerful tool should be used carefully and not abused in order to avoid painful situations.

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Online Casino Poker Gambling

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Craps Gambling Enterprise Game Of Chance

The much-appreciated casino site dice game of craps was formerly described as ‘crapaud’ as well as it is thought that the background of the start of this game can be traced back to the moment of the campaigns and since then it percolated to the French who promoted it worldwide. The significant requires of the craps casino site game of chance are a set of dice and also the gamers wager versus the casino site depending upon the outcome of a series of rolls of both dice or the outcome judi bola of a single roll.

Online Casino Poker Gambling

Craps is an incredibly popular game as well as besides casino sites, it is also commonly played throughout leisure times. The video game can be played by a solitary player and even numerous gamers. The game starts with the player turning out the two dice. According to the regulations, as it advances, if the total valuation of both the dice rolled amount to 2, 3,7,11, or 12, after that it signals that the round mores than and also a new round ought to be commenced right away. If the result of the roll is 2, 3, or 12, after that it is called ‘craps’. While, if the outcome is 11 or 7, after that it referred to as a ‘natural’ or ‘win’. However, it is to be born in mind that in instance, any type of other number excluding the above like 4,5,6,8,9 as well as 10 rollouts, then it is described as a ‘point’.

Real Gaming Stories

Under such circumstances, the shooter will need to proceed chancing time and again till the result of 7 is reached. In situation, the point circumstance is referred back to back, the round is wrapped up and a new game starts with the same shooter. If the gamer handles to rack up a 7 with the come-out roll, after that it is stated to be a ‘seven-out’ and that seals the round. A new game commences next with a brand-new shooter. The video game includes a collection of rounds and kumpulan situs judi bola terpercaya, sbobet link every single time the dice are presented for the very first time in each round, it is called ‘come-out roll’. The player that presents the dice, is referred to as ‘shooter’.

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Casino Poker Online

I’ve constantly liked playing online free online pokies win real money, yet it’s when I discovered that I might play casino poker online whenever I desired that was when I really loved it. Prior to I discovered playing texas hold’em on the net, I needed to wait till I obtained the opportunity to have fun with several of my close friend’s other halves, which had not been extremely usually. Since I have actually discovered online poker online, I can play a video game of online poker whenever I desire: texas hold’em as needed – it’s like paradise!

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You may be interested in the suggestion of going to a gambling enterprise however don’t recognize excessive concerning them – please continued reading for more information about the enjoyable of an evening bent on a casino site. Nevertheless, some video games such as casino poker are played with players versus gamers and in this instance, the online casino can not get an advantage as it is not effectively playing. In these conditions, the gambling establishment will take Situs Poker a “rake” on the wagers that players make versus each other.

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There is additionally another kind of poker betting found at casino sites known as video clip casino poker. Video clip texas hold’em is played by the exact same guidelines as normal casino poker, but it is a slot so you do not bet others, however rather attempt to obtain the best poker hand to win. Poker gaming is an exciting new hobby that many people of any age have begun just recently. Poker betting is a card game that includes both skill and also a little good luck. Figuring out the level at which you intend to play, specifically against the number of players on a website, is critical in Poker Online determining the most effective on-line texas hold’em rooms site for you.

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Casino Poker Pro Association

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Now that online football wagering is extensively available, football fans worldwide can sign up with the battle royal in a financial method. The smart money distances itself from nationalism and is always in search of one of the most unbiased football wagering suggestions. The best handicappers go far for themselves by rising above loyalties and also enthusiasms to provide mostly precise forecasts. In monetary markets and also bookmaking, there is no incentive for loyalty or partiality.

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Numerous people have actually been elevating the concern lately of authenticity and also whether or not football wagering is in fact worth your while. The what’s what is that there are lots of people that are truly good at betting on sports, and football particularly. Similarly, it can be claimed that there are lots of individuals that quit their money to the bookies. If you know what you are doing, football betting can be an enjoyable venture that pays big returns. Currently, you can obtain your football bets in without a lot of issues. The net has changed the method we do things for the better cara daftar sbobet. There are tons of sites since deal online football betting as well as generally they are legit businesses that treat their gamers with lots of respect.

Playing Texas Hold’em Online The Smart Way

There are many games to play and so much more time than an actual gambling establishment. These poker rooms are open throughout the day as well as evening, which enables you to play as long as you intend to. There are also games categorized for beginners as well as knowledgeable gamers that you can pick from. If you have actually not played texas hold’em until now, see among the online US texas hold’em spaces as well as experience the fun of playing casino poker video games! An online poker site is an online room like an online casino, where you Agen Poker QQ can play games, have a good time and also win or lose cash.

Excellent Texas Hold’em Present Ideas

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