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Crosson David dacr

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Functionnal programming ▪️ Scala ▪️ Kafka ▪️ Data ▪️ ZIO

dacr / gist:4559994

Last active December 11, 2015 06:29

scala 2.10.0, script example to illustrate how to get futures results as soon as they become available.

	#!/bin/sh
	exec scala -nocompdaemon -usejavacp -savecompiled "$0" "$@"
	!#

	/* will output :
	END of the script reached
	OK - slept 1s
	OK - slept 2s
	OK - slept 4s
	OK - slept 8s

dacr / gist:4634691

Created January 25, 2013 14:05

small test to check memory benefit of String substring change in Java 1.7.0_06

	#!/bin/sh
	exec scala -deprecation -nocompdaemon "$0" "$@"
	!#

	def usedMemoryInMo() = {
	val rt= java.lang.Runtime.getRuntime
	(rt.totalMemory - rt.freeMemory)/1024/1024
	}

	println(util.Properties.javaVersion)

dacr / gist:4642782

Last active July 9, 2020 11:02

Custom scala collection examples

	import scala.collection._
	import scala.collection.mutable.{ArrayBuffer,ListBuffer, Builder}
	import scala.collection.generic._
	import scala.collection.immutable.VectorBuilder



	// ================================ CustomTraversable ==================================

	object CustomTraversable extends TraversableFactory[CustomTraversable] {

dacr / gist:4718280

Created February 5, 2013 22:22

custom scala set collection example.

	// ============================= NamedCustomSet ===================================
	object NamedCustomSet {

	def apply[A](name:String, s:A*) = new NamedCustomSet(name, s.toSet)

	implicit def canBuildFrom[A,B]: CanBuildFrom[NamedCustomSet[B], A, NamedCustomSet[A]] =
	new CanBuildFrom[NamedCustomSet[B], A, NamedCustomSet[A]] {
	def apply(from: NamedCustomSet[B]) = newBuilder(from.name)
	def apply() = newBuilder
	}

dacr / gist:4749592

Last active December 12, 2015 09:09

1000 distinct remote ssh executions in 35s (1s required on each host)

	#!/bin/sh
	exec java -jar jassh.jar -nocompdaemon -usejavacp -savecompiled "$0" "$@"
	!#
	// jassh.jar can be downloaded here : http://code.google.com/p/janalyse-ssh/

	import jassh._

	import concurrent._
	import duration._
	import scala.util._

dacr / gist:5180825

Created March 17, 2013 09:39

list, view and stream - An example to understand the differences

	#!/bin/sh
	exec scala -deprecation -nocompdaemon "$0" "$@"
	!#

	val l=List(0, 1, 2)

	var x=1

	val m1=l.map(_ +x) // c1
	val v1=l.view.map(_+x) // c2

dacr / gist:5266909

Created March 28, 2013 21:20

Append a stream A to a stream B doesn't imply evaluation of all items of the first Stream A.

	#!/bin/sh
	exec scala -deprecation -nocompdaemon "$0" "$@"
	!#

	def trace(x:Int) = {println(x); x}

	val x=(1 to 5).toStream.map(trace _)
	// 1 is printed

	val y=(5 to 1 by -1).toStream.map(trace _)

dacr / gist:5322751

Last active December 15, 2015 20:59

Looking for the shortest (1 line only) and cleanest way to extract a map from a collection of parameters

	val args=Array("x=5", "y=10", "debug=true", "-verbose", "toto=truc1=titi", "nop", "tata=")

	val argsRE="([^=]+)=(.*)".r

	// ------- solution 1 with regex
	args.flatMap{case argsRE(k,v) => Some(k->v) case _=> None}.toMap

	// ------- solution 2 - with regex
	args.collect{case argsRE(k,v) => k->v}.toMap

dacr / gist:5437528

Created April 22, 2013 18:55

Play : Get ride of Thread.sleep to simulate remote processing

	package controllers

	import play.api._
	import play.api.mvc._
	import play.api.libs.concurrent.Execution.Implicits._
	import play.api.libs.concurrent.Akka
	import play.api.Play.current
	import scala.concurrent._
	import scala.concurrent.duration._

dacr / small-algo.scala

Created May 9, 2013 20:07

A small algorithm to find the indexof the first element superior or equal to the given value (in an ordered sequence)

	#!/bin/sh
	exec scala "$0" "$@"
	!#

	import scala.annotation.tailrec

	// ---------------------------------------------------
	def searchFirstGreaterOrEqual[T<%Ordered[T]](seq: Seq[T], value: T):Option[Int] = {
	@tailrec
	def binarysearch(left:Int, right:Int):Option[Int] = {