Use pattern matching (IDE0078 and IDE0260)

This article describes two related rules, IDE0078 and IDE0260.

#Overview

This style rule concerns the use of C# pattern matching constructs.

IDE0260 specifically flags the use of an as expression followed by a member read through the null-conditional operator. This rule is similar to IDE0019, which flags the use of an as expression followed by a null check.

#Options

Options specify the behavior that you want the rule to enforce. For information about configuring options, see Option format.

#csharp_style_prefer_pattern_matching (IDE0078)

#csharp_style_pattern_matching_over_as_with_null_check (IDE0260)

This option also configures rule IDE0019.

#Examples

#IDE0078

// csharp_style_prefer_pattern_matching = true
var x = i is default(int) or > (default(int));
var y = o is not C c;

// csharp_style_prefer_pattern_matching = false
var x = i == default || i > default(int);
var y = !(o is C c);

#IDE0260

// Code with violations.
object? o = null;
if ((o as string)?.Length == 0)
{
}

// Fixed code (csharp_style_pattern_matching_over_as_with_null_check = true).
object? o = null;
if (o is string { Length: 0 })
{
}

#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.

#pragma warning disable IDE0078 // or IDE0260
// The code that's violating the rule is on this line.
#pragma warning restore IDE0078 // or IDE0260

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

[*.{cs,vb}]
dotnet_diagnostic.IDE0078.severity = none
dotnet_diagnostic.IDE0260.severity = none

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

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

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

#See also

• C# 9.0 pattern matching
• Code style language rules
• Code style rules reference