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Use pattern matching to avoid 'as' followed by a 'null' check (IDE0019)

  • Article
Property Value
Rule ID IDE0019
Title Use pattern matching to avoid as followed by a null check
Category Style
Subcategory Language rules (pattern matching preferences)
Applicable languages C#
Options csharp_style_pattern_matching_over_as_with_null_check

Overview

This style rule concerns the use of C# pattern matching over an as expression followed by a null check. This rule is similar to IDE0260, which flags the use of an as expression followed by a member read through the null-conditional operator.

Options

The associated option for this rule specifies whether to prefer pattern match or an as expression with null checks to determine if something is of a particular type.

For more information about configuring options, see Option format.

csharp_style_pattern_matching_over_as_with_null_check

This option also configures rule IDE0260.

Property Value Description
Option name csharp_style_pattern_matching_over_as_with_null_check
Option values true Prefer pattern matching to determine if something is of a particular type
false Prefer as expressions with null checks to determine if something is of a particular type
Default option value true
C# 
// csharp_style_pattern_matching_over_as_with_null_check = true
if (o is string s) {...}

// csharp_style_pattern_matching_over_as_with_null_check = false
var s = o as string;
if (s != null) {...}

Suppress a warning

If you want to suppress only a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

C# 
#pragma warning disable IDE0019
// The code that's violating the rule is on this line.
#pragma warning restore IDE0019

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

ini 
[*.{cs,vb}]
dotnet_diagnostic.IDE0019.severity = none

To disable all of the code-style rules, set the severity for the category Style to none in the configuration file.

ini 
[*.{cs,vb}]
dotnet_analyzer_diagnostic.category-Style.severity = none

For more information, see How to suppress code analysis warnings.

See also