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README.markdown

A bunch of idiomatic, small General Purpose tools. This is totally experimental and undocumented for now.

Units

Time

import com.twitter.conversions.time._

val duration1 = 1.second
val duration2 = 2.minutes
duration1.inMillis // => 1000L

Space

import com.twitter.conversions.storage._
val amount = 8.megabytes
amount.inBytes // => 8192L
amount.inGigabytes // => 0.0078125

Futures

A Non-actor re-implementation of Scala Futures.

import com.twitter.util.{Future, Promise}

val f = new Promise[Int]
val g = f map { result => result + 1 }
f.setValue(1
g.get(1.second) // => This blocks for the futures result (and eventually returns 2)

// Another option:
g respond { result =>
  println(result) // => prints "2"
}

// Using for expressions:
val xFuture = Future(1)
val yFuture = Future(2)

for (
  x <- xFuture
  y <- yFuture
) {
  println(x + y) // => prints "3"
}

Collections

LruMap

The LruMap is an LRU with a maximum size passed in. If the map is full it expires items in FIFO order. Reading a value will move an item to the top of the stack.

import com.twitter.util.LruMap

val f = new LruMap[Key, Value](15) // this is of type mutable.Map[Key, Value]

Google MapMaker

import com.twitter.util.MapMaker

val map = MapMaker[Key, Value] { config =>
  config.weakKeys()
  config.weakValues()
} // this is of type mutable.Map[Key, Value]

Object Pool

The pool order is FIFO

A pool of constants

  val queue = new mutable.Queue[Int] ++ List(1, 2, 3)
  val pool = new SimplePool(queue)
  // Note that the pool returns Futures, it doesn't block on exhaustion.
  pool.reserve()() mustEqual 1
  pool.reserve { item =>
    println(item) // prints "2"
  }

A pool of dynamically created objects

Here is a pool of even-number generators. It stores 4 numbers at a time:

val pool = new FactoryPool[Int](4) {
  var count = 0
  def makeItem() = { count += 1; Future(count) }
  def isHealthy(i: Int) = i % 2 == 0
}

It checks the health when you successfully reserve an object (i.e., when the Future yields).

Eval

Dynamically evaluates Scala strings and files.

This is motivated by the desire to have a type-safe alternative to textual configuration formats such as YAML, JSON, or .properties files. Its advantages over these text formats are

  • Strong typing and compiler checking. If it doesn't compile and doesn't conform to the type you expect, you get an exception
  • The full power of Scala in your config. You don't have to use it. But you can.

in config/Development.scala

import com.xxx.MyConfig

new MyConfig {
  val myValue = 1
  val myTime = 2.seconds
  val myStorage = 14.kilobytes
}

in Main.scala

import com.xxx.MyConfig

val config = Eval[MyConfig](new File("config/Development.scala"))
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