Learning Kotlin: Introduction

Submitted by Robert MacLean on Mon, 06/11/2018 - 09:00

I have recently decided to start to learn Kotlin, and have started with the Koans.

Koans are simple unit tests which help ease you into learning a new language.

The first step was setting this up, in Windows and VSCode... cause for some reason I hate myself that much.

Requirements

Using

So I am using VSCode as the editor and then the command line to run the unit tests.

Parts

Since this will be ongoing, I am going to break it into a number of parts, listed below (this list will be updated over time):

  1. Hello World
  2. Java To Kotlin Converter
  3. Named Arguments
  4. Default Arguments
  5. Lambdas
  6. String Templates
  7. Data Classes
  8. Nullable Types
  9. Smart Casting
  10. Extension Functions and Extensions On Collections
  11. Object Expressions and SAM Conversions
  12. Kotlin's Elvis Operator
  13. Return when
  14. The awesome that is the backtick
  15. Collections
  16. It is a thing

Quick tip: Column display

Submitted by Robert MacLean on Fri, 06/08/2018 - 09:15

When you work with delimited data (CSV, TSV etc...) it can be a pain to just see the data in a nice way, for example, this data:

> cat people-example.csv.txt
First Name,Last Name,Country,age
"Bob","Smith","United States",24
"Alice","Williams","Canada",23
"Malcolm","Jone","England",22
"Felix","Brown","USA",23
"Alex","Cooper","Poland",23
"Tod","Campbell","United States",22
"Derek","Ward","Switzerland",25

With Unix like OSs, you can use the column command to format the layout; for example:

> column -t -s',' people-example.csv.txt
First Name  Last Name   Country          age
"Bob"       "Smith"     "United States"  24
"Alice"     "Williams"  "Canada"         23
"Malcolm"   "Jone"      "England"        22
"Felix"     "Brown"     "USA"            23
"Alex"      "Cooper"    "Poland"         23
"Tod"       "Campbell"  "United States"  22
"Derek"     "Ward"      "Switzerland"    25

With Windows, you can use Import-CSV and Format-Table in PowerShell:

> Import-Csv .\people-example.csv.txt | Format-Table

First Name Last Name Country       age
---------- --------- -------       ---
Bob        Smith     United States 24
Alice      Williams  Canada        23
Malcolm    Jone      England       22
Felix      Brown     USA           23
Alex       Cooper    Poland        23
Tod        Campbell  United States 22
Derek      Ward      Switzerland   25

SFTPK: Binary Search Tree

Submitted by Robert MacLean on Thu, 06/07/2018 - 09:00

This post is one in a series of stuff formally trained programmers know – the rest of the series can be found in the series index.

Binary Search Tree

In the previous post, we covered a Binary Tree, which is about the shape of storing the data. The Binary Search Tree (BST) is a further enhancement to that structure.

The first important change is that the data we are storing needs a key; if we have a basic type like a string or number then the value itself can be the key and if we have a more complex class, then we need to define a key in that structure or we need to build a unique key for each item.

The second change is a way to compare those keys which is crucial for the performance of the data structure. Numbers are easiest since we can easily compare which is larger and smaller.

The third and final change is the way we store the items; the left node's key will always be smaller than the parent nodes key and the right node's key will be larger than the parent node.

As an example, here is a BST using just numbers as keys:
A BST

Note that all nodes to the left are smaller than their parent and all parents above that.

Why?

So, why should we care about a BST? We should care because searching is really performant in it as each time you move a depth down, you eliminate approximately 50% of the potential nodes.

So, for example, if we wanted to find the item in our example with the key 66, we could start at the root (50) and move right. At that point, we have eliminated 8 possible nodes immediately. The next is to the left from the node with the 70 (total possible nodes removed 12). Next is to the right of the node with the value of 65, and then to 66 to the left of 67. So we found the node with 5 steps.

Going to Big O Notation, this means we achieved a performance of close to O(log n). It is possible to have a worst case of O(n), when the tree is not Optimal or Unbalanced.

Balanced versus Unbalanced

In the above example we have a binary search tree which is Optimal, i.e. it has the lowest depth needed. Below we can see a totally valid BST; Each child node is to the right of the parent because it is bigger than the parent.

Unbalanced BST

This, however, will result in a O(n) search performance which is not ideal. The solution is to rebalance the BST and for our example above we can end up with multiple end states (I'll show two below). The key takeaway is that we go from a depth of 5 to a depth of 3.

Balanced BST

Implementations

.NET has a built-in implementation with SortedDictionary. Unfortunately, nothing exists out of the box for this in JavaScript or Java.

Quick tip: Grep in Git

Submitted by Robert MacLean on Wed, 06/06/2018 - 09:00

This quick tip is about two small features of Git I wish I had known about earlier as it makes it way easier to do searching through it.

git-grep

git-grep is a way to search through your tracked files for whatever you provide. For example, if we want all files with the word index in it: git grep index

Demo of git grep

We can limit to specific files, for example, if we want to filter the above example to just JSON files: git grep index -- '*.json' Demo of git grep with filter

We can search for multiple items in a single file, for example, if we want to find all files with index and model in it: git grep --all-match -e index -e model Demo of git grep with multiple filters

git-log grep

git-log has a grep function too which is awesome for finding commit messages with a specific word or words in it. For example, if I want to find all commits about Speakers for DevConf I could do: git log --all --grep "Speaker"

Git log grep example

Drupal Geshi Cheatsheet

Submitted by Robert MacLean on Tue, 06/05/2018 - 14:16

Since redoing this blog, I switched out the syntax highlighting to use the Drupal Geshi Module.

For the love of everything I can't remember the tricks for using it, so here is a cheatsheet; mostly for myself but maybe you get value too. These are all HTML attributes you add can to your code block.

  • language this controls the language for rendering.
  • line_numbering controls if line numbering is off, on or fancy with the values off, normal and fancy respectively.
    • With fancy line numbers you can use the attribute interval to control how often to show the line numbers.
  • title adds a title to the code block.
  • special_lines takes a comma-separated list of numbers and highlights them.
  • linenumbers_start controls what the first line number is.

Information worked out from this code.

Quick tip: The handy command line calculator

Submitted by Robert MacLean on Tue, 06/05/2018 - 09:00

Who needs a GUI to do math when we have options for Unix like (MacOS, Linux etc...), Command Prompt, and PowerShell?

Unix like OSs

Unix OSs, including MacOS, WSL & Linux, include an awesome calculator called BC. From the man page:

bc is a language that supports arbitrary precision numbers with interactive execution of statements. There are some similarities in the syntax to the C programming language. A standard math library is available by command line option. If requested, the math library is defined before processing any files. bc starts by processing code from all the files listed on the command line in the order listed. After all the files have been processed, bc reads from the standard input. All code is executed as it is read.

The only cavet to use, is the file input; you can't just pass in parameters... but you can use echo to pass in the equation. For example:

> echo '1 + 2 + 3 + 4' | bc
> 10

bc can also work with different number bases, for example:

> echo "obase=2; ibase=10; 42" | bc
> 101010

obase stands for output base & ibase stands for input base. So in the example, we are turning 42 (base 10) to binary.

Floating point division is a weirdness with bc. For example, you would expect the answer to be 0.4 below but it is 0:

> echo "2/5" | bc
> 0

The solution is to use the math library switch -l:

> echo "2/5" | bc -l
> .40000000000000000000

and if 20 point position, you can use scale to control it:

> echo "scale=3; 2/5" | bc -l
> .400

Windows Command Prompt

Command prompt has a similar tool with the set command.

>set /a 3+3
6
>set /a (3+3)*3
18
>set /a "203>>3"
25

PowerShell

PowerShell natively supports some basic functionality, but if you want to use more advanced functionality you can use the entire System.Math class to do a lot of functionality.

> 4+5
9
> 6*7
42
> [Math]::Sin(50)
-0,262374853703929
> [Math]::Max([Math]::Tan(40), [Math]::Cos(40))
-0,666938061652262

Quick tip, the Say command

Submitted by Robert MacLean on Mon, 06/04/2018 - 09:00

MacOS has a great tool, called say which just says what you pass it. For example say "Hello" and next you'll hear your device say Hello.

Where this is really useful is when you want to do a long running action and get notified when it is done. For example git clone https://github.com/torvalds/linux.git && say "clone complete"


So, what about for Windows? You can do something similar with Powershell. First the setup:

Add-Type -AssemblyName System.speech
$say = New-Object System.Speech.Synthesis.SpeechSynthesizer

Once you have that in place you can use it like this: git clone https://github.com/torvalds/linux.git; $say.Speak("clone complete")

VSCode - Too many open files

Submitted by Robert MacLean on Thu, 05/31/2018 - 22:56

If you are getting the too many open files error with MacOS it could be VSCode trying to too many open files (or by default opening more than 10240 files).

You can confirm that with the following:

lsof |  awk '{ print $2 " " $1; }' | sort -rn | uniq -c | sort -rn | head -20

So, what can you do about it? If the files are not important, say it is your output folder, then you can use VSCode settings to exclude them. In the example below, I configure VSCode to ignore build folders. I would encourage this as a workspace setting, so everyone in the team gets it.

  1. // Configure glob patterns for excluding files and folders.
  2.   "files.exclude": {
  3.     "**/build": true
  4.   },
  5.  
  6.   "files.watcherExclude": {
  7.     "**/build": true
  8.   },
  9.  
  10.   "search.exclude": {
  11.     "**/build": true
  12.   },

MacOS utilities I find useful

Submitted by Robert MacLean on Thu, 05/31/2018 - 12:20

After using a MacBook Pro for two years I thought it was time to share what utilities I found really useful to have. These are obviously weighted towards being a software developer, so your mileage might vary.

Brew

It is the missing package manager for MacOS, so as with NPM, Chocolatey, or Composer, where you can install what you need via the command line.

It may seem weird, like what is wrong with just download and install what you need?! The advantage is that you can write this stuff down so that if you need to reinstall it is easier (and also easier to share to help others get up and running).

A second advantage is updating, it takes one command to update all the tools I use.

More info

VSCode

More than an IDE, this is my go-to tool for anything text; Editing config ✅taking notes ✅anything really.

Install with Brew: brew install homebrew/cask/visual-studio-code

An important tweak for VSCode is to make sure it is launching from the Terminal, thankfully it is really easy.

More info

Aerial

The AppleTV has the best screensaver I've ever seen, and some smart person ported it to MacOS with the name Aerial.

A word of warning, these videos are massive and will destroy your bandwidth. One tip to solve that is that under the settings is a Cache section - make sure you have the Cache Aerials As They Play checked else this will destroy your bandwidth. If you are on uncapped, then there is also a download now option which is a must to use.

Screen shot of screensaver settings

Install with Brew: brew install caskroom/cask/aerial

More info

Fish

Bash is nice, Fish is nicer. It just feels like what you expect in a modern world.

Install with Brew: brew install fish

More info

Fish Node Manager

Part of my job has involved working with multiple projects, and that means multiple versions of Node, and that was a pain. Thankfully there is a Node Manager for Fish that lets you easily change what version of Node you are using.

Unfortunately, this isn't as easy to setup, as to install it you first need Fisherman, which is like Brew but for Fish; which leads to this 3 step process to install it and configure it.

curl -Lo ~/.config/fish/functions/fisher.fish --create-dirs https://git.io/fisher
fisher fnm
fnm use latest

More info

Amphetamine

Amphetamine is a massively useful tool for MacOS, especially in a DevOps culture where you might get up in the night and just need your machine to behave the exact way you want it. Its core use is to not let your Mac go to sleep and you can control what triggers that, automatically or manually.

Get it from the Store

Status Clock

Another very useful tool is Status Clock which can show a second time on the menu which is exceptionally useful if you need to work across countries.

Get it from the Store

Settings Tweaks

Beyond useful tools, there are some useful tweaks to the standard MacOS settings:

SFTPK: Binary Tree

Submitted by Robert MacLean on Wed, 07/20/2016 - 18:25

This post is one in a series about stuff formally trained programmers know – the rest of the series can be found here.

Binary Tree

In the previous post we looked at the tree pattern, which is a theoretical way of structuring data with many advantages. A tree is just a theory though, so what does an actual implementation of it look like? A common data structure implementation is a binary tree.

The name binary tree gives us a hint to how it is structured, each node can have at most 2 child nodes.

Example of annotated binary tree

Classifications

As a binary tree has some flexibility in it, a number classifications have come up to have a consistent way to discuss a binary tree. Common classifications are: - Full binary tree: Each node in a binary tree can have zero, one or two child nodes. In a full binary tree each node can only have zero or two child nodes. - Perfect binary tree: This is a full binary tree with the additional condition that all leaf nodes (i.e. nodes with no children) are at the same level/depth. - Complete binary tree: The complete binary tree is where each leaf node is as far left as possible. - Balanced binary tree: A balanced binary tree is a tree where the height of the tree is as small a number as possible.

Implementations

While a binary tree is more than just a pattern, there are no out of the box implementations in C#, Java or JavaScript for it. The reason is that it is a very simple data structure and so if you need just the data structure you could implement it yourself but more importantly, you likely want more than the simple structure - you want a structure that optimises for traversal or data management.

References

Wikipedia: Binary Tree