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Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

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// Alternative to sealed abstract case class pattern for Scala 2.12.2+
// Benefits:
//  - 1 final class instead of 1 sealed class + anonymous subclass
//  - portable to Scala 3 regardless of opaque types
//  - less boilerplate

final case class Angle private (toDegrees: Int) {
  // Define our own `copy` method to suppress synthetic one
  // Add private to prevent it from being used
  def copy(degrees: Int = toDegrees): Angle = Angle.fromDegrees(degrees)

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How to use NonEmptyList in a model class

Let's say you are implementing an API and decide to return a base error response in common error situations such as BadRequest, NotFound etc.

final case class Error(code: String, description: String)

If you are returning an error response, your assumption would probably be that such responses should contain at least one error.

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jruby -S ast -e 'i += 1; i = i + 1'
AST:
RootNode 0
  BlockNode 0
    LocalAsgnNode:i 0
      CallNode:+ 0
        LocalVarNode:i 0
        ArrayNode 0
          FixnumNode 0
, null

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#!/usr/bin/env ruby -w
require "benchmark"

TIMES = 100_000
ARRAY = (1..1_000).to_a

Benchmark.bm(30) do |b|
  b.report "each" do
    TIMES.times do |i|
      ARRAY.each do |element|

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Puma::Plugin.create do
  def production?
    ENV.fetch('RACK_ENV', 'development') == 'production'
  end

  def log(msg)
    if production?
      Rails.logger.info msg
    else
      puts msg

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Applied Functional Programming with Scala - Notes

Copyright © 2016-2018 Fantasyland Institute of Learning. All rights reserved.

1. Mastering Functions

A function is a mapping from one set, called a domain, to another set, called the codomain. A function associates every element in the domain with exactly one element in the codomain. In Scala, both domain and codomain are types.

val square : Int => Int = x => x * x

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Shared State in pure Functional Programming

Newcomers to Functional Programming are often very confused about the proper way to share state without breaking purity and end up having a mix of pure and impure code that defeats the purpose of having pure FP code in the first place.

Reason why I decided to write up a beginner friendly guide :)

Use Case

We have a program that runs three computations at the same time and updates the internal state to keep track of the

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@ import $ivy.`org.typelevel::cats-effect:0.10.1` 

@ import cats._, cats.data._, cats.implicits._, cats.effect._, scala.concurrent.duration._, import scala.concurrent.ExecutionContext.Implicits.global

@ def lift(i: Int): IO[Int] = Timer[IO].sleep(1.second) >> IO { 
  
     println(Thread.currentThread.getName + "At time = " + java.time.Instant.now)
     i
  } 

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@ import $ivy.`org.typelevel::cats-effect:0.10.1` 

@ import cats._, cats.data._, cats.implicits._, cats.effect._

@ def lift(i: Int): IO[Int] = Timer[IO].sleep(1.second) >> IO { 
  
     println(Thread.currentThread.getName + "At time = " + java.time.Instant.now)
     i
  }