Tricks with Futures
class: center, middle
# Tricks with Futures
by Stephen Nancekivell
---
# Agenda
1. What are Futures
2. Tricks!
---
# What are Futures
---
# What are Futures
Data Type, container for a value,
```scala
class Future[T] {
...
}
```
```scala
val one = Future {
1
}
val two = Future {
Thread.sleep(1000)
2
}
```
---
# What are Futures
Data Type, container for a value,
```scala
class Future[T] {
def map[A](fn: T => A): Future[A]
}
```
---
# What are Futures
Data Type, container for a value,
```scala
class Future[T] {
def map[A](fn: T => A): Future[A]
}
```
```scala
val one = Future {
1
}
val two = one.map { oneValue =>
oneValue + 1
}
// Future(2)
```
---
# What are Futures
Data Type, container for a value,
```scala
class Future[T] {
def map[A](fn: T => A): Future[A]
def flatMap[A](fn: T => Future[A]): Future[A]
}
```
---
# What are Futures
```scala
class Future[T] {
def map[A](fn: T => A): Future[A]
def flatMap[A](fn: T => Future[A]): Future[A]
}
```
```scala
val futureId: Future[Int] = ???
def find(id: Int): Future[String] = ???
val result: Future[String] =
futureId.flatMap { id =>
find(id)
}
```
---
# Tricks
---
# Tricks
I have lots of futures and I want all of their values to work with at once.
---
# live coding
(βοΎβοΎ)β
---
```scala
def lotsOfFutures: Seq[Future[Int]] = ???
def wanted : Future[Seq[Int]] = ???
def sequence(xs: Seq[Future[Int]]): Future[Seq[Int]] = {
xs.foldLeft(Future(Seq[Int]())){ case (acc, item) =>
acc.flatMap { accValue =>
item.map { itemValue =>
accValue :+ itemValue
}
}
}
}
```
---
# Tricks
I am making too many futures at once, my database cant keep up!
---
# live coding
(βοΎβοΎ)β
---
```scala
def inputList: Seq[Int] = ???
def find(i: Int): Future[String] = ???
def wanted: Future[Seq[Int]] = ???
def traverse(xs: Seq[Int])(fn: Int => Future[String]): Future[Seq[String]] = {
xs.foldLeft(Future(Seq[String]())) { (acc, item) =>
acc.flatMap { accValue =>
fn(item).map { itemValue =>
accValue :+ itemValue
}
}
}
}
```
---
# Monads
Monads
Monads
---
# Monads
Monads
Monads
---
# Monads
```scala
class Future[T] {
def map[A](fn: T => A): Future[A]
def flatMap[A](fn: T => Future[A]): Future[A]
}
```
---
# Monads
```scala
class Future[T] {
def map[A](fn: T => A): Future[A]
def flatMap[A](fn: T => Future[A]): Future[A]
}
```
```scala
trait Monad[T] {
def map[A](fn: T => A): Monad[A]
def flatMap[A](fn: T => Monad[A]): Monad[A]
}
```
---
# Thank You
