https://developers.redhat.com/blog/2021/04/06/c-9-pattern-matching/

Red Hat Logo

  * Customer Portal
  * Developer
  * Hosted IDE
  * Marketplace
  * OpenShift
  * Partner Connect

  * Log In
  *  
  * Log Out

[logo]

RHD Navigation

  * Build Link to resources for building applications with open
    source software
  * Tools Link to developer tools for cloud development
  * Events Link to Red Hat Developer Events
  * Training Link to Red Hat Developer Training Content
  * Partners Connect with Red Hat: Work together to build ideal
    customer solutions and support the services you provide with our
    products.
  * Products Link to Red Hat Developer Products
  * [                    ]

Close

User account menu

  * Log in

[                    ]
RHD Navigation

  * Build Link to resources for building applications with open
    source software
  * Tools Link to developer tools for cloud development
  * Events Link to Red Hat Developer Events
  * Training Link to Red Hat Developer Training Content
  * Products Link to Red Hat Developer Products
  * [                    ]

Menu

Topic navigation

  * Istio
  * Quarkus
  * Kubernetes
  * CI/CD
  * Serverless
  * Java
  * Linux
  * Microservices
  * DevOps
  * All Topics

All Topics

Blog Articles

C# 9 pattern matching

tdeseyn
By Tom Deseyn April 6, 2021April 5, 2021
C# 9 pattern matching

The previous article in our C# 9 series looked at top-level programs
and target-typed expressions. In this article, we'll cover new
features for pattern matching. You can find an overview of the syntax
offered by previous versions of C# in C# 8 pattern matching.

Type patterns

When checking against a type, previous versions of C# required you to
include a variable name (or a _ discard). This is no longer required
with C# 9:

// is pattern with Type
if (input is Person)
...

// case pattern with Type
switch (input)
{
  case Person:
    ...

// is pattern with tuple Type
if (input is (int, string))
...

[2021_RHD_P]

Combining patterns

With the is expression in earlier versions of C#, you could already
combine patterns using regular logical operators:

if (person is Student || person is Teacher)
...

However, this doesn't work for switch expressions and switch case
labels. C# 9 adds support for combining patterns using the and and or
keywords, which works for both if and switch:

if (person is Student or Teacher)
...

decimal discount = person switch
{
   Student or Teacher => 0.1m,
   _ => 0
};

switch (person)
{
   case Student or Teacher:
      ...

The and patterns have higher precedence than the or patterns. You can
add parentheses to change or clarify the precedence.

Inverting patterns

With C# 9, you can invert patterns using the not keyword:

if (person is not Student)
...

switch (person)
{
  case not Student:
    ...

An interesting case is the is not null pattern. This will check
whether the reference is not null. Using != null may check something
different when the type overloads the != operator.

if (person is not null)
...

Relational patterns

Relational patterns allow you to compare an expression to a constant
numeric value:

decimal discount = age switch
{
   <= 2 => 1,
   < 6  => 0.5m,
   < 10 => 0.2m,
   _    => 0
};

Patterns within patterns

Patterns can also contain other patterns. This nesting lets you
express complex conditions in a concise and readable way. The
following example combines several types of patterns:

if (person is Student { Age : >20 and <30 })
...

Conclusion

In this article, we looked at the new pattern matching features in C#
9. The additions allow you to express more complex conditions with a
clear, concise syntax.

C# 9 can be used with the .NET 5 SDK, which is available on
Red Hat Enterprise Linux and Red Hat OpenShift, on Fedora, and from
Microsoft for Windows, macOS, and other Linux distributions.

Related

       Share

Categorized In

.NET, C#, Linux

Tags

.NET 5 C# 9

Recent Posts

  * Deploy Quarkus everywhere with Red Hat Enterprise Linux (RHEL)
  * Securely connect Red Hat Integration Service Registry with Red
    Hat AMQ Streams
  * C# 9 pattern matching
  * Get started with clang-tidy in Red Hat Enterprise Linux
  * Testing Apicurio Registry's performance and scalability
  * Design event-driven integrations with Kamelets and Camel K
  * Deploy integration components easily with the Red Hat Integration
    Operator
  * Get started with XDP
  * Security and management improvements in Red Hat JBoss Enterprise
    Application Platform 7.4 Beta
  * C# 9 top-level programs and target-typed expressions

Top Posts

  * How to install Python 3 on Red Hat Enterprise Linux
  * Top 10 must-know Kubernetes design patterns
  * How to install Java 8 and 11 on Red Hat Enterprise Linux 8
  * Introduction to Linux interfaces for virtual networking
  * Podman and Buildah for Docker users

Feeds

RSSATOM
Login to admin your blog

  * Featured Topics

      + Istio
      + CI/CD
      + Serverless
      + Enterprise Java
      + Linux
      + Microservices
      + DevOps
  * Build

      + Getting Started Center
      + Developer Tools
      + Hosted Che IDE
      + Interactive Tutorials
      + Container Catalog
      + Operators Marketplace
      + Certify Applications
      + Red Hat on Github
  * Quicklinks

      + What's new
      + DevNation events
      + Upcoming Events
      + Books
      + Cheat Sheets
      + Videos
      + Products
  * Communicate

      + Site Status Dashboard
      + Report a website issue
      + Report a security problem
      + Helping during COVID-19
      + About us
      + Contact Sales

Red Hat Developer

Build here. Go anywhere.

We serve the builders. The problem solvers who create careers with
code.

Join us if you're a developer, software engineer, web designer,
front-end designer, UX designer, computer scientist, architect,
tester, product manager, project manager or team lead.

  *  
  *  
  *  
  *  

Sign me up
Red Hat Logo

  * Copyright (c) 2018 Red Hat Inc.
      + 
      + Privacy Statement
      + Terms of Use
      + All policies and guidelines

Red Hat Summit

Privacy Preference Center

Options

  * Consent Management
  * Cookie Settings
      + Necessary
      + Analytics
      + Other

  * Privacy Policy

Consent Management

We use cookies on our websites to deliver our online services.
Details about how we use cookies and how you may disable them are set
out in our Privacy Statement. By using this website you agree to our
use of cookies.

Privacy Policy

Required 
We use cookies on our websites to deliver our online services.
Details about Red Hat's privacy policy, how we use cookies and how
you may disable them are set out in our Privacy Page. By using this
website you agree to our use of cookies.

Necessary

For ensuring site stability and functionality.

Cookies Used

Required 
__CT_Data, _CT_RS_, BIGipServer~prod~rhd-blog-http,
check,dmdbase_cdc, gdpr[allowed_cookies], gdpr[consent_types],
sat_ppv,sat_prevPage,WRUID,atlassian.xsrf.token, JSESSIONID,
DWRSESSIONID

Analytics

For site visitor traffic analysis

developers.redhat.com

Opt Out
_sdsat_eloquaGUID,AMCV_945D02BE532957400A490D4CAdobeOrg, rh_omni_tc,
s_sq, mbox, _sdsat_eloquaGUID,rh_elqCustomerGUID

Other

Disqus is used to facilitate comments on individual blog posts.

disqus.com

Opt Out
G_ENABLED_IDPS,NID,__jid,cpSess,disqus_unique,io.narrative.guid.v2,uuid2,vglnk.Agent.p,vglnk.PartnerRfsh.p
[Save Preferences]

OK