The other day, .NET 5 has been released. [^ dotnet5] .NET 5 supports C # 9. I'd like to try it immediately, but I don't want to install it on my PC, but I want to touch it a little, so I'd like to use Docker to prepare a disposable .NET 5 development environment.
Install Docker Try it on Play with Docker [^ pwd], a disposable Docker execution environment on the cloud that can be used with browsers that do not need to be installed.
The Linux environment of Play with Docker when executed is Alpine Linux 3.12, and the version of Docker is 19.03.11.
$ more /etc/issueWelcome to Alpine Linux 3.12
Kernel \r on an \m (\l)
$ docker --version Docker version 19.03.11, build 42e35e61f3
Run the .NET 5 SDK Docker image.
Connect the standard I / O to the shell with the -it option and board the .NET 5 SDK container as it is.
--rm option, the container is automatically deleted when the container is closed [^-rm].
If you try it on your PC, there will be no unnecessary containers left.$ docker run -it --rm mcr.microsoft.com/dotnet/sdk:5.0Unable to find image 'mcr.microsoft.com/dotnet/sdk:5.0' locally
5.0: Pulling from dotnet/sdk
bb79b6b2107f: Pull complete
97805e17b1a2: Pull complete
48d36279ea43: Pull complete
5d23a35fbf12: Pull complete
982bc1066a1e: Pull complete
6cc6e848c1f3: Pull complete
df97eda6f03d: Pull complete
7520ee234b82: Pull complete
Digest: sha256:ac49854ff6dcc1a2916ffc0981503f571698458187f925da0c2f2b6a0bec8dee
Status: Downloaded newer image for mcr.microsoft.com/dotnet/sdk:5.0
root@e68a47087ad8:/#
You can see that .NET 5 is installed.
root@e68a47087ad8:/# dotnet --version5.0.100
The Linux distribution seems to be Debian.
root@e68a47087ad8:/# more /etc/issueDebian GNU/Linux 10 \n \l
I would like to create a console app to try out the new features in C # 9.
root@e68a47087ad8:/# dotnet new console -o MyConsoleApp && cd MyConsoleAppGetting ready...
The template "Console Application" was created successfully.
Processing post-creation actions...
Running 'dotnet restore' on MyConsoleApp/MyConsoleApp.csproj...
Determining projects to restore...
Restored /MyConsoleApp/MyConsoleApp.csproj (in 89 ms).
Restore succeeded.
The project has been created.
root@e68a47087ad8:/MyConsoleApp# ls -R.:
MyConsoleApp.csproj Program.cs obj
./obj:
MyConsoleApp.csproj.nuget.dgspec.json MyConsoleApp.csproj.nuget.g.targets project.nuget.cache
MyConsoleApp.csproj.nuget.g.props project.assets.json
I want to edit the file, but vim is not included, so I would like to install it. First, update the package.
root@e68a47087ad8:/MyConsoleApp# apt update && apt upgradeGet:1 http://security.debian.org/debian-security buster/updates InRelease [65.4 kB]
Get:2 http://deb.debian.org/debian buster InRelease [121 kB]
Get:3 http://deb.debian.org/debian buster-updates InRelease [51.9 kB]
Get:4 http://security.debian.org/debian-security buster/updates/main amd64 Packages [248 kB]
Get:5 http://deb.debian.org/debian buster/main amd64 Packages [7906 kB]
Get:6 http://deb.debian.org/debian buster-updates/main amd64 Packages [7856 B]
Fetched 8401 kB in 1s (5711 kB/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
1 package can be upgraded. Run 'apt list --upgradable' to see it.
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
tzdata
1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 264 kB of archives.
After this operation, 3072 B of additional disk space will be used.
Do you want to continue? [Y/n] Y
Get:1 http://deb.debian.org/debian buster-updates/main amd64 tzdata all 2020d-0+deb10u1 [264 kB]
Fetched 264 kB in 0s (24.0 MB/s)
debconf: delaying package configuration, since apt-utils is not installed
(Reading database ... 9877 files and directories currently installed.)
Preparing to unpack .../tzdata_2020d-0+deb10u1_all.deb ...
Unpacking tzdata (2020d-0+deb10u1) over (2020a-0+deb10u1) ...
Setting up tzdata (2020d-0+deb10u1) ...
debconf: unable to initialize frontend: Dialog
debconf: (No usable dialog-like program is installed, so the dialog based frontend cannot be used. at /usr/share/perl5/Debconf/FrontEnd/Dialog.pm line 76.)
debconf: falling back to frontend: Readline
Current default time zone: 'Etc/UTC'
Local time is now: Sat Nov 14 16:16:39 UTC 2020.
Universal Time is now: Sat Nov 14 16:16:39 UTC 2020.
Run 'dpkg-reconfigure tzdata' if you wish to change it.
Install vim.
root@e68a47087ad8:/MyConsoleApp# apt install vimReading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
libgpm2 vim-common vim-runtime xxd
Suggested packages:
gpm ctags vim-doc vim-scripts
The following NEW packages will be installed:
libgpm2 vim vim-common vim-runtime xxd
0 upgraded, 5 newly installed, 0 to remove and 0 not upgraded.
Need to get 7425 kB of archives.
After this operation, 33.8 MB of additional disk space will be used.
Do you want to continue? [Y/n] Y
Get:1 http://deb.debian.org/debian buster/main amd64 xxd amd64 2:8.1.0875-5 [140 kB]
Get:2 http://deb.debian.org/debian buster/main amd64 vim-common all 2:8.1.0875-5 [195 kB]
Get:3 http://deb.debian.org/debian buster/main amd64 libgpm2 amd64 1.20.7-5 [35.1 kB]
Get:4 http://deb.debian.org/debian buster/main amd64 vim-runtime all 2:8.1.0875-5 [5775 kB]
Get:5 http://deb.debian.org/debian buster/main amd64 vim amd64 2:8.1.0875-5 [1280 kB]
Fetched 7425 kB in 0s (59.9 MB/s)
debconf: delaying package configuration, since apt-utils is not installed
Selecting previously unselected package xxd.
(Reading database ... 9877 files and directories currently installed.)
Preparing to unpack .../xxd_2%3a8.1.0875-5_amd64.deb ...
Unpacking xxd (2:8.1.0875-5) ...
Selecting previously unselected package vim-common.
Preparing to unpack .../vim-common_2%3a8.1.0875-5_all.deb ...
Unpacking vim-common (2:8.1.0875-5) ...
Selecting previously unselected package libgpm2:amd64.
Preparing to unpack .../libgpm2_1.20.7-5_amd64.deb ...
Unpacking libgpm2:amd64 (1.20.7-5) ...
Selecting previously unselected package vim-runtime.
Preparing to unpack .../vim-runtime_2%3a8.1.0875-5_all.deb ...
Adding 'diversion of /usr/share/vim/vim81/doc/help.txt to /usr/share/vim/vim81/doc/help.txt.vim-tiny by vim-runtime'
Adding 'diversion of /usr/share/vim/vim81/doc/tags to /usr/share/vim/vim81/doc/tags.vim-tiny by vim-runtime'
Unpacking vim-runtime (2:8.1.0875-5) ...
Selecting previously unselected package vim.
Preparing to unpack .../vim_2%3a8.1.0875-5_amd64.deb ...
Unpacking vim (2:8.1.0875-5) ...
Setting up libgpm2:amd64 (1.20.7-5) ...
Setting up xxd (2:8.1.0875-5) ...
Setting up vim-common (2:8.1.0875-5) ...
Setting up vim-runtime (2:8.1.0875-5) ...
Setting up vim (2:8.1.0875-5) ...
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/vim (vim) in auto mode
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/vimdiff (vimdiff) in auto mode
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/rvim (rvim) in auto mode
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/rview (rview) in auto mode
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/vi (vi) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/da/man1/vi.1.gz because associated file /usr/share/man/da/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/de/man1/vi.1.gz because associated file /usr/share/man/de/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/fr/man1/vi.1.gz because associated file /usr/share/man/fr/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/it/man1/vi.1.gz because associated file /usr/share/man/it/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ja/man1/vi.1.gz because associated file /usr/share/man/ja/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/pl/man1/vi.1.gz because associated file /usr/share/man/pl/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ru/man1/vi.1.gz because associated file /usr/share/man/ru/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/vi.1.gz because associated file /usr/share/man/man1/vim.1.gz (of link group vi) doesn't exist
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/view (view) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/da/man1/view.1.gz because associated file /usr/share/man/da/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/de/man1/view.1.gz because associated file /usr/share/man/de/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/fr/man1/view.1.gz because associated file /usr/share/man/fr/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/it/man1/view.1.gz because associated file /usr/share/man/it/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ja/man1/view.1.gz because associated file /usr/share/man/ja/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/pl/man1/view.1.gz because associated file /usr/share/man/pl/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ru/man1/view.1.gz because associated file /usr/share/man/ru/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/view.1.gz because associated file /usr/share/man/man1/vim.1.gz (of link group view) doesn't exist
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/ex (ex) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/da/man1/ex.1.gz because associated file /usr/share/man/da/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/de/man1/ex.1.gz because associated file /usr/share/man/de/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/fr/man1/ex.1.gz because associated file /usr/share/man/fr/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/it/man1/ex.1.gz because associated file /usr/share/man/it/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ja/man1/ex.1.gz because associated file /usr/share/man/ja/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/pl/man1/ex.1.gz because associated file /usr/share/man/pl/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ru/man1/ex.1.gz because associated file /usr/share/man/ru/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/ex.1.gz because associated file /usr/share/man/man1/vim.1.gz (of link group ex) doesn't exist
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/editor (editor) in auto mode
update-alternatives: warning: skip creation of /usr/share/man/da/man1/editor.1.gz because associated file /usr/share/man/da/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/de/man1/editor.1.gz because associated file /usr/share/man/de/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/fr/man1/editor.1.gz because associated file /usr/share/man/fr/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/it/man1/editor.1.gz because associated file /usr/share/man/it/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ja/man1/editor.1.gz because associated file /usr/share/man/ja/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/pl/man1/editor.1.gz because associated file /usr/share/man/pl/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/ru/man1/editor.1.gz because associated file /usr/share/man/ru/man1/vim.1.gz (of link group editor) doesn't exist
update-alternatives: warning: skip creation of /usr/share/man/man1/editor.1.gz because associated file /usr/share/man/man1/vim.1.gz (of link group editor) doesn't exist
Processing triggers for libc-bin (2.28-10) ...
Now that you're ready, let's try the C # 9 code. For details, please see the following article that I referred to.
** C # small story: Introducing favorite features in C # 9.0 that can be used with .NET 5.0 **
At the entry point, you can write code directly without a class. It seems to be convenient for simple batches.
root@e68a47087ad8:/MyConsoleApp# vim Program.csSystem.Console.WriteLine("Hello from top.");
Build. (Omitted in the following samples.)
root@e68a47087ad8:/MyConsoleApp# dotnet buildMicrosoft (R) Build Engine version 16.8.0+126527ff1 for .NET
Copyright (C) Microsoft Corporation. All rights reserved.
Determining projects to restore...
All projects are up-to-date for restore.
MyConsoleApp -> /MyConsoleApp/bin/Debug/net5.0/MyConsoleApp.dll
Build succeeded.
0 Warning(s)
0 Error(s)
Time Elapsed 00:00:02.44
root@e68a47087ad8:/MyConsoleApp# dotnet runHello from top.
You can easily create immutable objects.
Also, if the property values match, == will be true even for record types with different references.
You can also use the with expression to create a new record with only some properties rewritten, which I haven't tried in this article.
Creating value objects seems to be quick.
root@e68a47087ad8:/MyConsoleApp# vim Program.csusing static System.Console;
record Money(decimal amount);
class Program {
static void Main() {
var money1 = new Money(10);
WriteLine($"money1: {Money}");
var money2 = new Money(10);
WriteLine($"money2: {money2}");
WriteLine($"money1 == money2: {money1 == money2}");
}
}
root@e68a47087ad8:/MyConsoleApp# dotnet runmoney1: Money { amount = 10 }
money2: Money { amount = 10 }
money1 == money2: True
Target typed new[1]
You can omit the new type name when it is obvious by type inference.
Until now, there was a var inferred from the right side, but it could not be used in a member variable.
Also, it seems that the type name can be omitted even if the type is clear in the argument or return value.
using System.Collections.Generic;
using System.Linq;
class Program {
static readonly Dictionary<int, List<string>> _cache = new();
static void Main() {
_cache.Add(1, new() { "aaa" });
System.Console.WriteLine(_cache[1].First());
}
}
root@e68a47087ad8:/MyConsoleApp# dotnet runaaa
Or, and, not have been added to the conditional expression.
As a feature, it is evaluated once, so it seems easy to use for comparing the return values of expressions with side effects. (= It is no longer necessary to store the results in temporary variables and then compare them so that side effects do not occur multiple times)
Also, it seems that you can write it concisely together with pattern matching.
root@e68a47087ad8:/MyConsoleApp# vim Program.csusing static System.Console;
var x = 7;
WriteLine($"x is >= 5 and < 10: {x is >= 5 and < 10}");
WriteLine($"x is (<= 0 or 7 or <= 10) and not 15: {x is (<= 0 or 7 or <= 10) and not 15}");
object o = 2;
WriteLine($"o is int and >= 1: {o is int and >= 1}");
root@e68a47087ad8:/MyConsoleApp# dotnet runx is >= 5 and < 10: True
x is (<= 0 or 7 or <= 10) and not 15: True
o is int and >= 1: True
As I noticed later, every time I changed the source code, it was built by just dotnet run without dotnet build. Convenient.
Thank you for reading.
https://qiita.com/okazuki/items/8043ea6f0095b3019cdf#target-typed-new-%E5%BC%8F ↩︎
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