DEV Community: Robert Herdzik

What is `&+` operator for, and why Int8(127) &+ 1 is equal to -128

Robert Herdzik — Sat, 02 Jan 2021 09:21:58 +0000

Long story short

Scrolling through Apple Advanced Swift Operators documentation I encountered something 'interesting’. The case is that I have never used it, and neither see in the production code of the project to which I participated so far. I thought, let's play with this ‘just in case’.

My attention was caught by following operators:

&+ - Overflow addition
&- - Overflow subtraction
&* - Overflow multiplication

All of them has been created to deal with Integer overflow scenarios in our codebase.

What is Integer Overflow you may ask... is situation where: "an arithmetic operation attempts to create a numeric value that is outside of the range that can be represented with a given number of digits – either higher than the maximum or lower than the minimum representable value.", we are going to explain it using example later on 😎.

I know that is not a common case, but it is good to have at least an idea that some API for handling mentioned computation in Swift is waiting for us. In this article we are going to focus only on &+, since rest of them works in the simmilar manner.

YouTube already failed with `Integer overflow`

Researching quickly about the topic of Integer overflow, I found one funny story related to the YouTube website, and how they failed with assumption, that 'Int32' is going to be enough to store ‘view count’ for each video. Yep, they took the following assumption, and it was working for them for a long time, but suddenly crazy viral Psy’s “Gangnam Style” video came, and destroyed they ‘view count’ layout, because mentioned video exceeded value, which is able to be stored by 'Int32' variable, mean that music video surpassed over 2,147,483,647 views. After admitting that they made a mistake, the view counter type has been switched to 'Int64' which can store enormous 9,223,372,036,854,775,807 (gosh… that’s over 9 quintillion) views.

Scenarios in which simple `+` operator is not enough

As an example we can use 'Int8' (signed 8-bit integer) type, which can store values from -128 to 127.

Normally if we do simple calculation like:

let a: Int8 = 127
let b: Int8 = 1
let sum = a + b // Compilation error 💥

We get a smart compilation error which says that: “Arithmetic operation ‘127 + 1’ (on type ‘Int8’) results in an overflow”, that is great! Seems that we are covered… unfortunately, compilator is going to help us only in that kind of static/obvious scenario, let's consider other scenarios where he won't be that helpful:

func makeValue() -> Int8 { 1 }

let a: Int8 = 127
let b: Int8 = makeValue()
let sum = a + b // Runtime error 💥

That scenario is giving us "Thread 1: Swift runtime failure: arithmetic overflow” runtime error, plus beautiful app crash. 😪

Overflow addition to the rescue!

We can consider once again the first example but with &+ operator in action.

let a: Int8 = 127
let b: Int8 = 1
let sum = a &+ b // Compilator is OK with this 🤓

As we can see, compilation went smoothly, but the result of the calculation is quite unexpected at the first glance, because after checking 'sum' constant value, we see -128, what the heck!

To understand better this operator, we can do manual 'Int8' addition with the deliberate overflow, bit by bit.

Taking our 127 number, which is the maximum positive value of 'Int8' type, where binary representation is: 0111 1111 , most significant bit (MSB) has 0 value (0 for positive, and 1 for negative numbers). And 'Int8(1)' binary representation is: 0000 0001. Knowing this let`s do Overflow addition:

Ok! Everything is now clear, &+ operator in this calculation flipped to 1 our MSB bit, and in result we get a binary value of 1000 0000 which in context of 'Int8' type has -128 value.

Is there any easy way to react in Unit Tests on type Overflow cases?

For creating Unit Tests which can check Type Overflows, we could use the 'addingReportingOverflow' method, which as a result returns a tuple of operation value, and 'Bool' value which indicates whether operation has been finished with overflow or not.
let result = Int8.max.addingReportingOverflow(1)
'result' is an tuple, which has following values for presented scenario: (partialValue -128, overflow true)

Original article source: LINK

Resources

SkrybaMD - generate project documentation with ease

Robert Herdzik — Sun, 25 Oct 2020 14:02:18 +0000

Github project source: LINK.

intro

Let's start first from the point which will clarify whether this blog post is for you, or is a total waste of your precious time, having this established, you can dive deep into it, or go back to your favorite 9gag section ;)

You should spend your time reading this article if:

you want to maintain your documentation in Markdown (.md) format
if you want to have clear process to generate .md documentation
you work in the team (more than one dev which would like to take care of documenting stuff), or you just love to manage your .md document in consistent/ease way
you are tired of manual intended management in your documentation content
many times you were blocked to add some point of your documentation, straight in the middle, due to the necessity to modify manually further sections punctuation in the doc (I have facet this a lot!)

...ok, now we have clear, and you can decide whether to read further or just skip it.

what is SkrybaMD for?

SkrybaMD is a very simple, Swift powered documentation generator. Is fully open source, so you are able to contribute, or post your ideas related to the script there. Look for it here.

is it hard to use it?

Honestly I need to say, that is really straightforward to use!

Steps to follow:
1 . install it using e.g. brew:
$ brew install robertherdzik/homebrew-SkrybaMD/SkrybaMD

Note, that more installation options you can find in the github repo Readme
2 . create shape doc_shape.txt file
3 . in doc_shape.txt create corresponding three structure with your sub document files names, like:

i || General || general.md
i || Architecture || architecture_config.md
ii || Our Approach || our_approach.md
i || CI and Rest || ci_and_rest.md
i || Summary || summary.md

4 . execute in your doc_shape.txt directory $ SkrybaMD MySuperDocumentationFileName terminal command, and you are done!
Skryba will generate, final documentation output file, with consistent look and feel, as well you will get e.g. Table of Content for free there. Now each time you or your team member wants to modify, he needs to only update ‘shape’ file and regenerate documentation using mentioned terminal command.

You can find in here how automatically generated documentation looks like base on the doc_shape.txt file.

NOTE
Additionally you can specify some more parameters once you use SkrybaMD, please check README to see the latest functionalities of the scrypt.

is it hard to get rid of it, once I decide to do so?

The case is that, since as an output, you get a final .md documentation file, you just stop using SkrybaMD, and can go back to manual documentation shaping. So as you can see, this script is totally not addictive at all for your project/workflow.

Original article source LINK

Saying sorry to Vim

Robert Herdzik — Fri, 02 Oct 2020 10:07:59 +0000

Saying sorry to Vim

Some time ago, I decided to stop being ignorant in the area of Vim text editor, mainly due to playing with my raspberryPi or pushing myself more into using git via terminal mainly, you have to believe me, that Vim skills are welcome not only for these use cases.

Key thing to know is that this powerful editor is available on most Linux distributions by default, if not, you can easily install it.

Do you see this... learn it once, and you are using it everywhere. There is also a crazy amount of plugins which you can additionally install, to make your flow even more pleasant.

C'mon, also as an engineer, we need to know at least how to ‘exit’ from the vi document. I believe that even basic knowledge of Vim will buy you a lot of time in your day to day work, and for sure you will look more ‘pro’.

First step

With a very fundamental level of Vim knowledge, I started to explore the quickest paths to learn more, and I have found a nice tweet, which was promoting very cool looking platform game, using which, in easy, and funny way I was able to refresh my memory, and learn more shortcuts. The name of the game is VIM Adventures, and you can find it here #highlyRecommend. After some time with the game, I started to feel comfortable with the editor once again, and in this way I could force myself more toward Vim, during my day to day work.

Gluing a short cheat sheet, base on my needs

We can't estimate how much you need to know upfront, so I didn't even want to create a collection of cheat sheet shortcuts upfront, I decided that I do it, once I face the need to use a particular feature of Vim (incremental approach to creating my personal cheat sheet). This technique is commonly known as YAGNI in software development, funny thing, but I apply this rule quite often, even in my life.

Please find below all shortcuts which I have found useful for me, for sure list is going to grow with the time (maybe good idea would be to put it in github repo 🤔).

My base cheat sheet

Help

:help keyword - open help for keyword

Create/save file

vi {fileName} - create/open file from Terminal
:q - exit without saving
:q! - force exit without saving (in case you have changes, which needs to be ignored)
:wq - save and exit
:w - save only

Navigation

h, j, k, l - move cursor
H - move cursor to top of visible page
M - move cursor to middle of visible page
L - move cursor to bottom of current page
w - jump to the beginning of next word
b - jump to the beginning of the current word
e - jump to the end of current word
G - end of file
gg - beginning of file
$ - end line
0 - beginning of line
A - end of line + edit mode

Deletion

dd - delete whole line
dw - delete word
x - remove character

New line

o - insert new line below
O - insert new line above

Undo/reUndo

u - undo
ctrl + r - reUndo

Find Word

:set hlsearch - enable highlight search matches
:nohlsearch - disable highlight search matches
:/{Word to match} - n navigate forward, N navigate backward

Copy/paste terminal internally

v select block
y copy
Press P to paste before the cursor, or p to paste after

Cut/paste internally

Position the cursor where you want to begin cutting.
Press v to select characters (or uppercase V to select whole lines).
Move the cursor to the end of what you want to cut.
Press d to cut (or y to copy).
Move to where you would like to paste.
Press P to paste before the cursor, or p to paste after.

Select

V - whole block
v - and navigate (using h, j, k, l) to select part of the text

Visual features

:set number - show line number
:set nonumber - hide number

Practicing

The most important thing of course, is to practice! At the beginning it was very hard to start, because there is a huge temptation to move back to the UI driven text editor, but with time you will cross this thin line, and then Vim becomes quite intuitive, and is going to be your ‘go to’ editor.
I’m constantly learning, and extending my knowledge in this area, I’m so excited each time, when I notice that it has an feature which I was missing using e.g. Sublime.

More sources to explore Vim

Home | Vim Cheat Sheet

For sure, that someone else created Vim Cheat Sheet before, here you can find quite broad library of shortcuts.

Tutorial with main combination

Another interactive way of learning, I didn’t use it, but I believe that is worth mentioning here. It presents the editor in a very easy to digest way!

VIM Adventures game

Yep, I have just mentioned this game in the post.

Cristopher Okhravi tutorial

If you prefer to learn from video, Christopher Okhravi, has a crazy nice YT series about Vim, also I strongly recommend to check his other videos where e.g. he is explaining SOLID principles in a very precise way.

Original post: Link

DEV Community: Robert Herdzik

What is `&+` operator for, and why Int8(127) &+ 1 is equal to -128

Long story short

YouTube already failed with Integer overflow

Scenarios in which simple + operator is not enough

Overflow addition to the rescue!

Is there any easy way to react in Unit Tests on type Overflow cases?

Resources

SkrybaMD - generate project documentation with ease

intro

what is SkrybaMD for?

is it hard to use it?

is it hard to get rid of it, once I decide to do so?

Saying sorry to Vim

Saying sorry to Vim

First step

Gluing a short cheat sheet, base on my needs

My base cheat sheet

Help

Create/save file

Navigation

Deletion

New line

Undo/reUndo

Find Word

Copy/paste terminal internally

Cut/paste internally

Select

Visual features

Practicing

More sources to explore Vim

YouTube already failed with `Integer overflow`

Scenarios in which simple `+` operator is not enough