Forem: Andrei Fedotov

What's new in C# 10? New features of C# 10

Andrei Fedotov — Tue, 26 Oct 2021 16:38:01 +0000

File-scoped namespace declaration

In C# 9 Top Level Statement feature was introduced. It allows in the app's entry point file not to write a boilerplate code.

Instead of the following:

namespace HelloWorld
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
        }
    }
}

It's enough only one line of code vs ten.

Console.WriteLine("Hello World!");

And it was amazing but having such ability only in one place does not bring much profit especially in a big project. So, C# 10 goes further and it brings a feature with the name File-scoped namespace declaration.

Let's consider an example. We have a project. It contains two classes. We see that the class is declared inside the namespace. It is inside the curly braces

namespace _1._File_Scoped_Namespace
{
    public class Author
    {
        public string Name { get; set; }
        public string LastName { get; set; }
        public Author(string name, string lastname) =>
            (Name, LastName) = (name, lastname);
    }
}

File-scoped namespace declaration allows to get rid of the curly braces and make the code even more elegant. After the namespace, we need to put the semicolon.

namespace _1._File_Scoped_Namespace;
public class Author
{
    public string Name { get; set; }
    public string LastName { get; set; }
    public Author(string name, string lastname) =>
        (Name, LastName) = (name, lastname);
}

Extended property patterns

A new feature which is called Extended property patterns is highly useful for the conditions with nested properties.

Let's see in action. We have a Book class. And we want to implement a method that will tell us if the book has a discount.

    public static bool doesHaveDiscount(Book book)
    {
        return false;
    }

Let's agree if the author's last name matches the specific value then we have a discount, otherwise, we don't.

public static bool doesHaveDiscount(Book book) =>
        book switch
        {
            { Author: { LastName: "Richter" } }
                or { Author: { LastName: "Price" } } => true,
            _ => false
        };

We see nested properties of the author's object. Now we can simplify this construction by accessing the property with the dot.

public static bool doesHaveDiscount(Book book) =>
    book switch
    {
        { Author.LastName: "Richter" }
            or { Author.LastName: "Price" } => true,
        _ => false
    };

It makes the code more readable and cleaner.

Constant interpolated strings

Strings iInterpolation is very cool because we can put the object right inside the string without leaving its borders.

public string ThankYouMessage()
{
    return string.Empty;
}

Let declare two variables. And make an interpolation for the second one.

var message = "Thank you for buying the book!";
var thankYouMessage = $"{message} Enjoy";

In C# 10 we can declare those strings as the constants because it is obvious that the values are not intended to change.

public string ThankYouMessage()
{
    const string message = "Thank you for buying the book!";
    const string thankYouMessage = $"{message} Enjoy";
    return thankYouMessage;
}

Records

One of the features of C# 9 was the record types. Long story short they allow to make classes immutable. C# 10 goes further and now we can create record structures. Let's consider the immutable structure

public readonly record struct Point
{
    public int X {  get; }
    public int Y {  get; }
}

After the name of the structure, we can pass the parameters.

public readonly record struct Point(int X, int Y);

and get rid of the rest of the code.

Also, in C# 10 we have the ability to add the sealed keyword while overriding the ToString() method in a record type. It tells the compiler: "don't create ToString() for all inherited types, use this one".

record Circle
{
    public sealed override string ToString()
    {
        return typeof(Circle).Name;
    }
}

Assignment and declaration in the same deconstruction

The next feature is related to deconstruction. In previous versions, we could assign the values while deconstruction, or we could initialize them first and then assign them.

internal class Author
{
    public string Name { get; set; }
    public string LastName { get; set; }
    public Author(string name, string lastname) =>
        (Name, LastName) = (name, lastname);

    public void Deconstruct(out string name, out string lastname) =>
        (name, lastname) = (Name, LastName);

    public override string ToString() =>
        $"{Name} {LastName}";
}

var author = new Author("Andrei", "Fedotov");
Console.WriteLine(author);

(string name1, string lastName) = author;
Console.WriteLine(name1);
Console.WriteLine(lastName);

var name2 = string.Empty;
var lastname2 = string.Empty;
(name2, lastname2) = author;
Console.WriteLine(name2);
Console.WriteLine(lastname2);

C# 10.0 removes that restriction.

var lastname3 = string.Empty;
(var name3, lastname3) = author;
Console.WriteLine(name3);
Console.WriteLine(lastname3);

Global using directives

One more feature is Global using directives.

If importing the same namespaces in each app's file is annoying you then this feature is for you. C# 1- allows mark the imports as global and they will be imported into the files automatically,

global using System.Collections.Generic;
global using System.Linq;

namespace _6._Global_Using_directive;
public class Store
{
    private readonly IEnumerable<Book> Books;
    public Store(IEnumerable<Book> books) => Books = books;
    public IEnumerable<Book> GetBooks(Author author) =>
        Books.Where(b => b.Author.LastName == author.LastName);
}

Moreover, in the project configuration, there is a flag to enable implicit usings.

<ImplicitUsings>enable</ImplicitUsings>

Improvements of structure types

Since C# 10 we can declare the parameterless constructor for the structures.

public struct Point
{
    public Point()
    {
        X = double.NaN;
        Y = double.NaN;
    }
    public Point(double x, double y) =>
        (X, Y) = (x, y);

    public double X { get; set; }
    public double Y { get; set; }

    public override string ToString() =>
        $"X: {X}, Y: {Y}";
}

var point = new Point(1,2);
Console.WriteLine(point); // X: 1, Y: 2

var point2 = new Point();
Console.WriteLine(point2); // X: NaN, Y: NaN

var point3 = default(Point);
Console.WriteLine(point3); // X: 0, Y: 0

default ignores the parameterless constructor and gives the default value for a type.

The repo with the examples is here.
Thank you for reading the post, I hope you enjoyed it.
You also might want to check C# 9 list of features.

Cheers!

List of C# 9 features

Andrei Fedotov — Tue, 29 Jun 2021 23:48:29 +0000

Top-level statements

The very simple program on C# looks like the following

using System;
namespace HelloWorld
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
        }
    }
}

but with C# 9 we can make it simpler:

System.Console.WriteLine("Hello World!");

Target-Typed Object Creation

Let's imagine we have a class:

public class Book
{
    public string Title { get; set; }
    public string Author { get; set; }

    public Book()
    {

    }

    public Book(string title, string author)
    {
        Title = title;
        Author = author;
    }
}

Usually we create objects like follow:

var book = new Book();
// or
Book book = new Book();

With C# we can do:

Book book2 = new();
Book book3 = new("1", "A1");

Init-only Setters

Consider we have a class Book

public class Book
{
        public string Title { get; set; }
        public string Author { get; set; }
}

and we can set values during the initialization. At the same time we can change the values as far as we have a setter for every field as well.

var book = new Book { Author = "1", Title = "2" };
book.Title = "2";

Imagine a situation where we want only set values during the initialization and we want to restrict them after initialization. In C# 9 Init-only feature comes into play:

public class Book
{
        public string Title { get; init; }
        public string Author { get; init; }
}

var book = new Book { Author = "1", Title = "2" };
book.Title = "2"; // compile error

Relational & Logical Patterns

Relational patterns permit the programmer to express that an input value must satisfy a relational constraint when compared to a constant value

public class Book{  public string Title { get; set; }   public string Author { get; set; }  public static decimal Postage(decimal price) => price switch    {       < 20 => 6.99m,      >= 20 and < 40 => 5.99m,        >= 40 and < 60 => 2.99m,        _ => 0  };}

Records

We have a class:

public class Book{    public string Title { get; }    public string Author { get; } public Book(string title, string author)    {          Title = title;          Author = author;    }}

And let's imagine we want to be able to create a book. We can do it as following:

var book = new Book("Title1", "Author1");

and also we want to serialize the object and de-serialize

var json = JsonSerializer.Serialize(book);Console.WriteLine(json);var book2 = JsonSerializer.Deserialize<Book>(json);var isEqual = book == book2;Console.WriteLine($"book == book2: {isEqual}"); // false

In console we'll see that de-serialized book is not the same book that was serialized. How can we make them the same? We can override equals operator:

public static bool operator ==(Book left, Book right) =>    left is object ? left.Equals(right) : right is null;

if we override == operator we also have to override !- operator:

public static bool operator !=(Book left, Book right) => !(left == right);

But we have not done anything to compare our object yet, so we have to override Equals method:

public override bool Equals(object obj) => obj is Book b && Equals(b);public bool Equals(Book other) => other is object &&  Title == other.Title && Author == other.Author;

And we need to override GetHashCode and ToString methods.

public override int GetHashCode() => HashCode.Combine(Title, Author);public override string ToString() => $"{Title} - {Author}";

Also, we have to make our class implement IEquatable<T> interface.

public class Book : IEquatable<Book>

Finally we have to write a bunch of code for just one simple action. Full class:

public class Book : IEquatable<Book>{   public string Title { get; }   public string Author { get; }   public Book(string title, string author)   {       Title = title;       Author = author;   }   public static bool operator ==(Book left, Book right) =>       left is object ? left.Equals(right) : right is null;   public static bool operator !=(Book left, Book right) => !(left == right);   public override bool Equals(object obj) => obj is Book b && Equals(b);   public bool Equals(Book other) =>       other is object &&       Title == other.Title &&       Author == other.Author;   public override int GetHashCode() => HashCode.Combine(Title, Author);}

Now Console.WriteLine($"book == book2: {isEqual}"); will output true.

There is a lot of boilerplate code.

Moreover, if we add a new field we will have to update every method.

With C# 9 we can use the record type for the same behavior. It allows making behavior for classes as if they were structures.

record Book(string Title, string Author)

Extended partial methods

Now we can use modifiers and return values for partial methods.

public partial class Book{  public string Title { get; set; }   public string Author { get; set; }  public decimal Price { get; set; }  private partial decimal SetPrice();}public partial class Book{  private partial decimal SetPrice()  {       return 0m;  }}

Covariant returns

In C# 9 we can return derived types in overridden methods.

public class Book{  public string Title { get; set; }   public string Author { get; set; }}public class CollectionBook : Book{  public string Edition { get; set; }}public abstract class BookService{  public abstract Book GetBook();}public class CollectionBookService : BookService{   public override CollectionBook GetBook()    {       return new CollectionBook();    }}

Code: https://github.com/platinum-team/tech-talk-csharp9-features

Cheers!

C# Ranges and Indexes

Andrei Fedotov — Tue, 22 Jun 2021 13:38:01 +0000

Intro

In this tutorial, we're going to go through two new .NET types - System.Index, System.Range and cover appropriate operators: ^ and ...

If you are interested in learning more about C# language, this is for you.

You’ll be able to use the skills and lessons in this tutorial in the real dev world when you work on any project using C#.

It will provide you with a more elegant way to work with sequences and laconic syntax to access elements. Long story short - to use modern language constructions to write easily readable and understandable code.

Ranges and Indexes were introduced as part of .NET Standard 2.1. This is C# 8 feature. It is available in .NET 5, netcore 3.0. It is not supported by .NET Framework. It can be applied for arrays, spans, and readonly spans.

Preparations

First, go to your favorite IDE, it might be Visual Studio, VS Code, Rider, LINQPad, etc. Make sure to start with nothing open or running (except your computer!) I prefer Visual Studio

Next, create a new project and go through the steps.

Steps

The dataset I’m going to use for this tutorial is just a string array of languages.

Create a collection. Let's create an array with the languages.

var languages = new string[] { "Spanish", "English", "Japanese", "French", "German", "Russian", "Italian", "Korean", "Chinese" };

Index

How can we get the second element - "English"? It is pretty easy to do, we just have to pass the index (remember that the numeration if indexes in collections in C# starts from 0)

int index = 1;
var english = languages[index];
Console.WriteLine(english); // Output: English

Instead of int variable we can use Index type for doing the same:

Index index1 = 1;
var english2 = languages[index1];
Console.WriteLine(english2);

Here is another way to create index. Index is value type so when we do new Index() it will set the default value to 0

var index2 = new Index(); // zero by default because this is a structure
var spanish = languages[index2];
Console.WriteLine(spanish);

We can pass the index value as a parameter to the constructor

var index3 = new Index(2);
var japanese = languages[index3];
Console.WriteLine(japanese);

Probably for now you might ask what is the benefit to use index rather than just integer variable? Okay, probably for accessing the first or second elements there are no many benefits. But in the next examples, we will see getting the last element and will see much more benefits when we will try indexes with ranges together.

The second question here is how can we get the last element? Okay, we can simply get the length of the array and subtract 1. (because of the first element has the index 0 that's way the last element has the index last element - 1)

var lastIndex1 = languages.Length - 1;
var chinese1 = languages[lastIndex1];
Console.WriteLine(chinese1);

And the same by using Index:

Index lastIndex2 = ^1;
var chinese2 = languages[lastIndex2];
Console.WriteLine(chinese2);

We can do both above examples in one line.

Console.WriteLine(languages[languages.Length - 2]); // Korean

Console.WriteLine(languages[^2]); // Korean

The struct Index has overwritten method Equals so we can check the equality of the two indexes.

var equals = index1.Equals(index2);
Console.WriteLine(equals); // false

Range

Usually, users are forced to implement complex structures to filter/operate on slices of memory or resort to LINQ methods like list.Skip(5).Take(2). With the addition of System.Span<T> and other similar types, it becomes more important to have this kind of operation supported on a deeper level in the language/runtime and have the interface unified.

Range operator .. is a binary infix operator that accepts two expressions, or both expressions can be omitted.

Range myRange1 = 1..4;

This can be used with indexes together:

Index start = 1;
Index end = 4;
Range myRange2 = start..end;

The following will output the 1, 2 and 3 elements from array:

string[] languagesRange = languages[1..4];
foreach (var language in languagesRange)
{
    Console.WriteLine(language);
}

A bit more interesting usages.

3 last elements:

string[] languagesRange1 = languages[^3..];

From start to pre-last element (every except the last one)

string[] languagesRange2 = languages[..^1];

3 elements before pre-last element

string[] languagesRange3 = languages[^4..^1];

As I mentioned earlier the same we can do with Span

Span<string> languagesSpan = languages;
Span<string> selectedLanguagesSpan = languagesSpan[1..4];
foreach (var language in selectedLanguagesSpan)
{
    Console.WriteLine(language);
}

Thank you

Thank you very much for reading. I hope it brought something new to you. Hope you'll find a chance to give it a try for these features in your projects. Also, I would appreciate any feedback from you. Feel free to post your comments below.

The source code can be found here.

How to create a new folder in visual studio - keyboard shortcuts

Andrei Fedotov — Tue, 15 Jun 2021 17:31:22 +0000

Hello everyone!

Creating a new folder in Visual Studio manually (by using the mouse) is a bit annoying process. I like to use shortcuts for such kinds of routines. And this note shows several options for how to create a new folder in Visual Studio by using shortcuts.

Option 1

Ctrl+Alt+L - switch focus to Solution Explorer
Press one at a time Alt, p, d

Option 2

If you use Resharper for Visual Studio

Alt+Shift+L to focus on Solution Explorer
Alt+Ins to create a folder

Option 3

Set your own shortcuts

Go to Tools -> Options -> Environment -> Keybord
Select Project.NewFolder and set hot keys

Option 4 (my choice)

Use VS extension Add New File

Press Shift+F2 to open a dialog and type a file name. The most exciting thing here is by using / you can also create a folder structure where the file will be placed.

Cheers!

How to change GitHub Actions run_number

Andrei Fedotov — Tue, 08 Jun 2021 15:31:57 +0000

Hello everyone!

What we have

We use the well-known schema for versioning the product builds:

major.minor[.build[.revision]]

For example: 3.2.1234.0.

We use GitHub Actions for CI/CD needs. We use GitHub's run_number value as a build number.

The challenge

Recently we faced a challenge to set an offset for different types of build (e.g. production/test builds).

Searching over the internet had a lack of answers to the question of how to change run_number or how to increment it.

The solution

After a good bit of time spent on documentation investigation, we came up with a solution. Assume run_number is 1000. And we want the build number to be 5000. And the final product version we want to have 3.2.5000.0 We can do the following as separate step in the workflow:

    steps:  
    - name: Set version number
      run: |
        $version = "3.2."+(4000+$($Env:GITHUB_RUN_NUMBER))+".0"
        echo $version
        echo "VERSION_NUMBER=$version" | Out-File -FilePath $Env:GITHUB_ENV -Encoding utf-8 -Append

That's it. Now the variable VERSION_NUMBER contains the value 3.2.5000.0.

And we can use that value across the workflow like this (e.g. we construct installer package name that containing the version):

MyProduct.${{ env.VERSION_NUMBER }}.msi.

Hope this would be helpful for you.

Cheers!

Launching Angular app on emulator without Android Studio

Andrei Fedotov — Mon, 29 Jun 2020 00:45:27 +0000

Previously we went through launching Android emulator without installing Android studio. In this note we will launch Angular application on that emulator.

First, what we need to do is we have to install build tools by sdkmanager in order to be able to build applications :

sdkmanager "build-tools;29.0.3"

Also we can add %ANDROID_HOME%\emulator and %ANDROID_HOME%\platform-tools as the entries into Path variable to improve the experience. It will allow us to run emulator and adb commands from any directory in command line. Just use Start -> Edit the system environment variables -> Environment variables... -> Path -> New for doing that.

Prepare a NativeScript project for running

If you haven't install nativescript cli yet, you can do it by executing the following command:

npm install -g nativescript

Next, create new project from scratch:

tns create HelloWorld --template tns-template-blank-ng
cd HelloWorld

This is just an example of angular application for running. You can use your own app for this.

Run the emulator

Type the following to see a list of available emulators:

avdmanager list avd

We'll see something like:

Available Android Virtual Devices:
    Name: test_avd_29
    Path: C:\Users\Andrei_Fedotov\.android\avd\test_avd_29.avd
  Target: Google APIs (Google Inc.)
          Based on: Android 10.0 (Q) Tag/ABI: google_apis/x86_64
  Sdcard: 512 MB

Next, let's run the emulator:

emulator -avd test_avd_29

Okay, emulator is working. What we are gonna be doing next is we are just gonna be launching the app on that emulator.

To see a list of available emulators we can use adb:

$ adb devices

Output:

List of devices attached
emulator-5554   device

Or we can use tns :

tns device

Output:

By using one of above commands we can know a Device Identifier for launching the app on emulator.

Next, let's use the following command to launch the app:

tns run android --device emulator-5554

After building we'll see the app launched

Troubleshooting

If you're receiving the error Failed to open /qemu.conf, err: 2, try to create this file by executing echo # > c:\qemu.conf and launch cmd as administrator.

Cheers!

Notes - How to become a Product Manager

Andrei Fedotov — Sat, 27 Jun 2020 22:13:16 +0000

Recently I've listened to talks on GitCommitShow. One of them was about becoming a product manager by Gaurav Nemade. I really enjoyed his speech. So I made notes for myself according to what he talked about. But I suppose perhaps these notes would also be helpful for someone else.

The speaker focuses on two points:

What exactly is the job of a Product Manager
Getting into product management

Let's go over the points.

What exactly is the job of a Product Manager

Let's imagine that we are developing an application. What the app is gonna be doing is it is just gonna be helping people to play the guitar.

What game should we be playing? (aka define the product strategy)

What kind of solution should we build?
1. A peer-to-peer network of tutors & learners (Uber for guitar learning)
2. A collection of guitar chords (wikipedia for guitar learning)
3. A tutor app with coaching functionality (Karoake style app for guitar learning)
What is the goal for company & project?
1. Increase users; ear more revenues; side project out of interest
What are the core user needs & segments?
1. What are user pain points and needs?
2. Should we target the amateur players of advanced guitar players?
How is the overall industry & trend?
1. What's the value proposition of Ultimate Guitar, Yousician & others.
2. What new technologies are that can help improve guitar learning.

Prioritization of Efforts

What game are we playing -> Build a guitar tutoring app for newbies with a goal of building user base.

Next we are listing the whole bunch of features we want to build.

Features to build

Library of chords
Lessons with progressive difficulty
Record what user is playing
Pick mistakes by using a ML model
25 others...

What we need to do next is just to decide which features we want to see first and choose them; which features we can develop later; and perhaps some feature not actual anymore during the work. So I understand it as a kind of prioritizing.

Features to build

Library of chords [Phase-1]
Lessons with progressive difficulty [Phase-1]
Record what user is playing [Dropped]
Pick mistakes by using a ML model [Phase-2]
25 others...

Balancing act

User requests
Business needs
Best for the product (short-term vs long-term)

A good phrase is: "If Everything Is a Focus, Nothing Is A focus"

Product manager's responsibility is to define what is in a focus.

Execution

At the end of the day, Product Manager ships products and they do whatever else it takes.

A. Clear specifications on what to build and why

B. Analyze user data

If there is no data analyzer then it is PM's responsibility.

Which lessons are being played the most? Add them as features lessons?

C. Quality Analyst of the product

Learn to play guitar and test the product everyday.

D. Interface with (or fill in for) x-functional needs

Running marketing campaign, working with lawyers to build privacy policies, working with UX, partnerships team and more.

Getting into product management

The question is "Should I be a Product Manager?"

"It depends!", the speaker says.

The positives and the challenges of being a PM

Positives

Solving a real-world problem
- Front and center of identifying problems to solve
Breadth vs depth
- Broad exposure to industry, competitive products, x-functional teams (Design, Sales, Marketing, Legal, etc.)
Leadership training
- "What" & "Why" in development cycle (vs SWEs primary focus on "How")
- People skills

Challenges

Lack of tangible skills
- PMs rely a lot on intagible skills
Leading w/o authority
- PMs almost never have direct authority over SWE team and have to work with influence.
Busy than most other roles
- Have to work with different areas
- Meeting are a way of life no (or very less) coding
"If it succeeds, it's because of the team. If it fails, it's because of you (the PM)"

Prepping to be a PM

Product & strategic Insights: Build your product insights & strategic insights by studying loads of case studies and being curios about products around you
Communication skills: Develop negotiation (& preferrably) public speaking skills.
Understand different types of PM roles: B2C vs B2B, Hardware vs Software, Front end vs backend technology PM, etc.
Prepare well for interviews: different companies have different interview process (common themes are product & strategic insights, analytical, creativity, communication as main criteria).

Strategy: THINK LIKE A PM - "What would I do if I were the PM of the product?" (So PM thinks this way for every product they see)

All these wonderful things I caught in Gaurav's talk.

Cheers!

How to install Android emulator without installing Android Studio

Andrei Fedotov — Fri, 08 May 2020 16:45:24 +0000

This is the step-by-step note that answering the question: How to install and launch Android emulator without installing Android Studio itself.

Download and install JDK
Set JAVA_HOME variable.

Open Command Prompt (Win+R, type cmd and press Enter) or use any other terminal you like. For me path to JDK is E:\Program Files\Java\jdk1.8.0_251. Execute the following:
```
setx JAVA_HOME "E:\Program Files\Java\jdk1.8.0_251"
```
or use Start -> Edit the system environment variables -> Environment variables... -> New...
Download and install Intel Hardware Accelerated Execution Manager (HAXM) (you also need to switch off Hyper-V feature and enable Virtualization in BIOS for successful installation).
Download Command-Line-Tools: Go to Downloads page , scroll down to "Command line tools only" section and download the archive with tools.
Go to AppData\Local:
```
cd %localappdata%
```

Create the following folder structure and go inside:

mkdir Android\cmdline-tools
cd Android\cmdline-tools

Extract downloaded commandlinetools-win-*_latest.zip folder into cmdline-tools folder:
```
tar -xf C:\Users\a\Downloads\commandlinetools-win-6200805_latest.zip
```
Starting from Android SDK Command-line Tools 1.0.0 (6200805), in contrast to Android SDK 26.1.1 (4333796), the tools directory hierarchy has been changed. Previously it was placed right inside ANDROID_HOME, now it's still named as tools (the only thing you'll get after unpacking the downloaded commandlinetools zip file), but differently, you have to place it inside a directory called cmdline-tools on your own.

The structure is supposed to be the following:

├── cmdline-tools
   └── tools
       ├── bin
       ├── lib
       ├── NOTICE.txt
       └── source.properties

Set ANDROID_HOME environment variable:

setx ANDROID_HOME %localappdata%\Android

Create new entry in Path environment variable:
```
setx path "%PATH%;%ANDROID_HOME%\cmdline-tools\tools\bin" /m
```
Note: you'll probably need to restart cmd in order the changes take effect.
The next command allows us to see the list of available packages:
```
sdkmanager --list
```
We need to install such packages like platform-tools, platforms;android-* and system-images;android-*;google_apis;x86_64, where * means the version:
```
sdkmanager "platforms;android-29" "system-images;android-29;google_apis;x86_64" "platform-tools"
```
Next we have to accept a bunch of licenses. Type the next command and answer y to each question:
```
sdkmanager --licenses
```

Now we are ready to create new virtual device:

avdmanager create avd -n test_avd_29 -k "system-images;android-29;google_apis;x86_64"

To see the list of virtual devices just type:
```
avdmanager list avd
```
Go to emulator folder:
```
cd %ANDROID_HOME%\emulator
```
Last but not least thing is launching:
```
emulator -avd test_avd_29
```

Cheers!

Shell script that finds all files which correspond to a given template

Andrei Fedotov — Fri, 15 Nov 2019 17:53:33 +0000

Hello everyone!
Welcome to an ideological continuation of our journey to 1969 year.

Introduction
In today’s short trip we will develop a program with using of shell language. We won’t to use find command. Our program will search all files whose names correspond to a given template. The search will be in a given sub-tree of the file structure.

The result of the execution will be a list of the names of the desired files on the screen. The program will consist of two scripts. The first is the main script. It displays the prompt to enter the path name for initial directory and ask to type the search template (mask). Then it performs the input of this data from the keyboard and displays a list of the searched files in the initial search directory (if there are any). Then it calls a nested script for each subdirectory, passing it two input parameters: the relative name of the subdirectory and the search pattern.

Let’s go!

First, create files in the directories so that the script can work with them.

Next, create two files: "search" and "runsearch". The first one is a search program, and the second is designed to run.

Add the following code to "runsearch" file (the code's explanation is below):

read  p "Catalog: " catalog
set -f
read -p "Search mask: " mask
sh ~/../home/admin/dirC/search "$catalog" "$mask"

Add the following code to "search" file:

cd "$1"
set +f
for name in *
do
if [ -d "$name" ]
then
set -f
sh "$0" "$name" "$2"
set +f
else
if test "${name#*$2}" != "$name"
then
echo $name
fi
fi
done

You can do it with old-school text editor like ED editor

Code explanation
$1 – refers to the first argument given to the script at execution. For the script executed in the following manner: sh search catalog mask, it refers to the catalog name given as a first argument;
$2 - refers to the second argument (mask);
$0 - refers to the name of the script (search);
set -f is the portable (i.e. POSIX) way to disable filename expansion.
When it is enabled (by default or with set +f), filename expansion is an operation performed by the shell that replaces, when possible, command line arguments containing:
• occurrences of wildcards (? = any single character and * = any number of characters)
• ranges enclosed in square brackets (e.g. [a-z12] = any character from a to z, or 1 or 2)
• non-matching lists (e.g. [^a-z] = any character not in the range a to z)
• and character classes (e.g. [[:xdigit:]] = any character that can be used to represent an hexadecimal number)
by the file names that match them.
When disabled, these arguments are left unchanged.

Let's move next. Do scripts executable:
chmod +x ./.runsearch
chmod +x ./.search

Make sure that they have become such (displayed in a different color).

Let’s check the work of script for different directories.

So, as we see when we run the script it asks us to input the catalog name and search mask. In the result it gives us the list of files which correspond to the mask in the given directory and sub-directories.

Conclusion
We have developed a script that searches in a given subtree of the file structure of all files whose names correspond to a given template.

Cheers!

Back to 1969 or Introduction to Ed - old-school text editor

Andrei Fedotov — Sun, 01 Sep 2019 03:46:44 +0000

1969
What happened in 1969 Major News Stories include The Beatles' last public performance, on the roof of Apple Records, First Concorde test flight is conducted In France, Boeing 747 jumbo jet makes its debut, Pontiac Firebird Trans Am the epitome of the American muscle car is introduced, Woodstock attracts more than 350,000 rock-n-roll fans, Members of a cult led by Charles Manson murder five people, Chappaquiddick Affair Senator Edward Kennedy, PBS Established, The first man is landed on the moon on the Apollo 11 mission by the United States and Neil Armstrong and Edwin 'Buzz' Aldrin became the first humans to set foot on the Moon.
But there is one more thing ... Awesome string-line text editor: ed. Let's immerse in the atmosphere of the late 1960s and touch the history.

History
As early as 1969, the first assembly-language version of ed was in place. Although later rewritten in C, the editor is fundamentally the same program as used then. As Kernighan and Plauger wrote in 1976, The earliest traceable version of the editor presented here is TECO, written for the first PDP-1 timesharing system at MIT.

PDP-1:

It was subsequently implemented on the SDS-940 as the "quick editor'" QED by L. P. Deutsch and B. W. Lampson.

SDS-940:

K. L. Thompson adapted QED for CTSS on the IBM 7090 at MIT.

IBM 7090:

Later D. M. Ritchie wrote a version for the GE-635 at Bell Labs.
The latest version is ed, a simplified form of QED for the PDP-11, written by Ritchie and Thompson.

PDP-11:

This is not to say that ed is the same as the TECO found on some DEC computers. For one thing, TECO is character oriented while ed is line oriented. It seems rather a case of "common ancestry".
During the 1970's, the editor went through countless revisions. Nearly every university had its own modified versions of ed and qed; some had several modified versions. Jay Michlin of Bell Labs wrote (in IBM assembler) a QED for IBM's mainframe TSO; this was released to Universities in the mid-70's.
And, of course, ed would visit Berkeley and, while there, mutate into ex and vi.
Let's taste it.
During our today’s journey we will consider simple operations with Ed and after we will develop the script that performs the following actions: displaying a list of files that are “children” of a given directory that have a given character set in their names and destroying all other files of a given directory. In the end we will create initializing script that will say hello after login and run another script for searching files.

Simple operations of Ed
Let’s create two three-level directories for our experiments.
mkdir -p {dirA,dirB}/dir1/dir2
Now we have the following structure (can be output to console with the help of tree command):

.
├── dirA
│   └── dir1
│       └── dir2
└── dirB
    └── dir1
        └── dir2

Create four text files in one of the directories.
cd dirA cd dir1 cd dir2 touch file1.txt file2.txt file3.txt file4.txt

Adding the text to a file with ed.
Let’s edit the file with ed. Launch it with the filename as a parameter:
ed file1.txt
In case when file does not exist ed creates a new one. If it already exists, then ed tells us the length of file. In our case the length is zero. In order to add text to the file we have to switch to adding mode by “a” command.
It appends text to the buffer after the addressed line. The current address is set to last line entered.
An address represents the number of a line in the buffer. ed maintains a current address which is typically supplied to commands as the default address when none is specified. When a file is first read, the current address is set to the last line of the file. In general, the current address is set to the last line affected by a command.
So, let’s switch to adding mode:
a
And type some words:
Hello!
This is text form file1!
To exit from adding mode type point on the new line:
.
To write changes type:
w
it prints new size of file. In order to quit from ed:
q

Adding text to the beginning, middle and to the end of file.
Let's complicate the task a bit and add text to the beginning, middle and end of the file.
Open file again. Let’s print the addressed line by ‘p’ command. It prints us ‘This is a text from file1!’. It’s easy to add the text to the end of file right now. Just switch to adding mode by ‘a’ command and print ‘End’.
Done! Now exit from adding mode by printing ‘.’. To print the first line of document type ‘1p’. It also set the current address to the number of first line. Now we can print ‘i’ command to switch to ‘Insert mode’. This magic command inserts text before the current line and the current address is set to the last line entered. So, after switching to insert mode, let’s type ‘Start’. Then, on the new line type ‘.’ to exit from insert mode. Let’s set the current address to the line number 3. In order to do this just type ‘3p’. Now we can switch to insert mode again and add text to the middle of document.
In order to print the whole text from file type the following:
1, $p
Further save file and quit from ed. Step-by-step way is represented in the picture below.

Let’s copy file with the help of ‘cp’ command.

Super finder script
Let’s make the challenge more complicated and develop the script for searching files, which are located in all subdirectories of the current directory, which have in their name a given character set. Then display these files and destroy all other files of a given directory. The script will fart with two parameters. The first parameter is catalog name and the second is the set of symbols (mask). For testing let’s create files in the directories.

Run the script to execute. After check the contents of the directories.

Initialization script
Let's develop our initialization script, which say hello by rewriting shell invitation.
Create file “.bashsrc” and edit it in ED editor.

In order to check do logout and login into the system back.

Let's perfect our script so that it also runs the nested script created earlier and passes the directory name and part of the file name as parameters to it. And check his work.

So, we plunged into the atmosphere of the 1960s, I hope it was fun. That’s it. Thank you!
Cheers!

Fix of Angular-cli 'JavaScript heap out of memory' error while running 'ng serve'

Andrei Fedotov — Thu, 17 Jan 2019 10:11:42 +0000

First option:
Run node command as:
node --max_old_space_size=8048 ./node_modules/@angular/cli/bin/ng serve
where 8048 is new memory limit in megabytes (by default it's ~1500).

Or add the command to package.json file:

"build-serve": "node --max_old_space_size=8048 ./node_modules/@angular/cli/bin/ng serve"

and run as npm run build-serve

Second option:
The quick and effective solution for Windows
Open C:\Users\userName\%AppData%\Roaming\npm
Copy/paste the following code into ng.cmd:

@IF EXIST "%~dp0\node.exe" (
    "%~dp0\node.exe" --max_old_space_size=8048 "%~dp0\node_modules\@angular\cli\bin\ng" %* 
) ELSE (
    @SETLOCAL 
    @SET PATHEXT=%PATHEXT:;.JS;=;% 
    node --max_old_space_size=8048 "%~dp0\node_modules\@angular\cli\bin\ng" %* 
)

UPD (7 May 2020)
Third option:
Set it as an environment variable.
SET NODE_OPTIONS=--max_old_space_size=8048
Thanks to @jonyadamit for sharing

Cheers!

How to join several commits into one?

Andrei Fedotov — Sat, 12 Jan 2019 18:00:59 +0000

First way:

1) Consider we have the following commit’s history:

* 493f284 2019-01-11 | fourth (HEAD -> master) [Andrei Fedotov]
* d2fd771 2019-01-11 | second 3 [Andrei Fedotov]
* 4ad568e 2019-01-11 | second 2 [Andrei Fedotov]
* 1c29a96 2019-01-11 | second 1 [Andrei Fedotov]
* ca8ad26 2019-01-11 | first [Andrei Fedotov]

and we want to join second 1, second 2 and second 3 commits into one commit named second.
Execute the next command:

git rebase -i HEAD~4

2) After that the window with commits list will open in order of their creation (up to down):

pick 1c29a96 second 1
pick 4ad568e second 2
pick d2fd771 second 3
pick 493f284 fourth

3) Commits that we want to join with the previous commit we have to mark as squash. Commits which we want to stay without changes we stay as pick

pick 1c29a96 second 1
squash 4ad568e second 2
squash d2fd771 second 3
pick 493f284 fourth

4) Save and close the window. The next window will open where we should type the message for our joined commit. As a result, we obtain:

* 7a98610 2019-01-11 | fourth (HEAD -> master) [Andrei Fedotov]
* 5ef60fc 2019-01-11 | second [Andrei Fedotov]
* ca8ad26 2019-01-11 | first [Andrei Fedotov]

Another way:

1) Imagine we added one more commit and we want to join two last commits to one:

* 865a0f6 2019-01-11 | third (HEAD -> master) [Andrei Fedotov]
* 7a98610 2019-01-11 | fourth [Andrei Fedotov]
* 5ef60fc 2019-01-11 | second [Andrei Fedotov]
* ca8ad26 2019-01-11 | first [Andrei Fedotov]

2) Type the following commands:

git reset --hard HEAD~2
git merge --squash HEAD@{1}
git commit

3) Type the name of the commit in the opened window. For example: third. Now we have:

* c79f494 2019-01-11 | third (HEAD -> master) [Andrei Fedotov]
* 5ef60fc 2019-01-11 | second [Andrei Fedotov]
* ca8ad26 2019-01-11 | first [Andrei Fedotov]

If the commits we merged were pushed to the server before, we have to update them. It’s possible by typing the next command:

git push origin +branch_name

In addition, we can use helpful and convenient alias:
Bash:

git config --global alias.squash '!f(){ git reset --soft HEAD~${1} && git commit --edit -m"$(git log --format=%B --reverse HEAD..HEAD@{1})";};f'

Cmd:

git config --global alias.squash "!f(){ git reset --soft HEAD~${1} && git commit --edit -m\"$(git log --format=%B --reverse HEAD..HEAD@{1})\";};f"

Now it is possible to use this command to combine the last N commits:

git squash N

Cheers!