IO

---
# Actions requirements

## 2. Can fail
]

## -> Try

]

---
# Actions requirements

## 2. Can fail

## 3. Async
]

## -> Try

## -> Execute on a thread pool
]

---
# By-name parameters

```scala
def onError[A](action:` => A`, callback: Throwable => Any): A =
    ???
```
]

---
# By-name parameters

```scala
def onError[A](action: => A, callback: Throwable => Any): A =
    ???
```

```scala
object Try {
  def apply[A](action:` => A`): Try[A] =
    ???
}
```

```scala
object Future {
  def apply[A](action:` => A`)(implicit ec: ExecutionContext): Future[A] =
    ???
}
```
]

---
# Action encoding

---
# Action encoding

.fifty-two-left[
```scala
object Action {
  def apply[A](action:` => A`): Action[A] =
    ???
}
```
]

---
# Action encoding

.fifty-two-left[
```scala
object Action {
  def apply[A](action: => `A`): Action[`A`] =
    ???
}
```
]

---
# Action encoding

}
```
]

---
# Action encoding

.fifty-two-left[
```scala
object Action {
  def apply[A](action:` => A`): Action[A] =
    ???
}
```
]

}
```
]

---
# Action encoding

.fifty-two-left[
```scala
object Action {
  def apply[A](action: `() => A`): Action[A] =
    ???
}
```
]

}
```
]

---
# Action encoding

.fifty-two-left[
```scala
object Action {
  def apply[A](action: () => A): Action[A] =
    ???
}
```
]

def greeting(): Unit =
  println("Hello")
```
]

}
```
]

---
# Action encoding

---
# Action encoding

.fifty-two-left[
```scala
object Action {
  def apply[A](action: => A): Action[A] =
    new Action[A] {
      def execute(): A = `???`
    }
}
```
]

---
# Action encoding

.fifty-two-left[
```scala
object Action {
  def apply[A](action: => A): Action[A] =
    new Action[A] {
      def execute(): A = action
    }
}
```
]

---
# Comparison

greeting()
// Hello

greeting()
// Hello
```
]

```scala
def greeting(): Unit  =
  println("Hello")

greeting()
// Hello

greeting()
// Hello
```
]

```scala
val greeting: Action[Unit] =
  Action{ println("Hello") }

greeting.execute()
// Hello

greeting.execute()
// Hello
```
]
]

---
# Rich API

def retry(maxAttempt: Int): Action[A] = ???

def onError(cb: Throwable => Any): Action[A] = ???

def parallel(ec: ExecutionContext) = ???
}
```
]

---
# Documentation

.fifty-seven-left[
```scala
def getUser(id: Long): Action[User] =
  db.query(s"SELECT * from USERS where id = $id")

val greeting: Action[Unit] =
  Action { println("Hello") }
```

```scala
def sum(x: Int, y: Int): Int =
  x + y
```
]

---
# Ordinary value

.fifty-seven-left[
```scala
def getUser(id: Long): Action[User] =
  db.query(s"SELECT * from USERS where id = $id")

val getBob = getUser(1234)
val getEda = getUser(9753)

val actions = List(getEda, getBob)

actions.foreach(_.execute())
// res: List[User] = List(
//   User(9753, Eda, ...),
//   User(1234, Bob, ...),
// )
```
]

---
# Naming convention

```scala
object Action {
  def apply[A](action: => A): Action[A] =
    new Action[A] {
      def execute(): A = action
    }
}
```
]
.forty-seven-right[
```scala
trait IO[A] {
  def unsafeRun(): A
}
```

```scala
object IO {
  def apply[A](action: => A): IO[A] =
    new IO[A] {
      def unsafeRun(): A = action
    }
}
```
]

---
# Naming convention

```scala
object Action {
  def apply[A](action: => A): Action[A] =
    new Action[A] {
      def execute(): A = action
    }
}
```
]
.forty-seven-right[
```scala
trait `IO`[A] {
  def unsafeRun(): A
}
```

```scala
object IO {
  def apply[A](action: => A): IO[A] =
    new IO[A] {
      def unsafeRun(): A = action
    }
}
```
]

---
# Naming convention

```scala
object Action {
  def apply[A](action: => A): Action[A] =
    new Action[A] {
      def execute(): A = action
    }
}
```
]
.forty-seven-right[
```scala
trait IO[A] {
  def `unsafeRun`(): A
}
```

```scala
object IO {
  def apply[A](action: => A): IO[A] =
    new IO[A] {
      def unsafeRun(): A = action
    }
}
```
]

---
class: white

# .white[Summary]

## .white[Encode action with a trait (SAM)]

## .white[Constructor with a by-name parameter]

## .white[Provide a rich API (retry, onError)]

---
background-image: url(../img/fp-tower/website-background-white.svg)

## package exercises.action.fp.console

# UserCreationService.scala