Use pattern matching (IDE0078 and IDE0260)

Članak
27. 07. 2023.

This article describes two related rules, IDE0078 and IDE0260.

Property	Value
Rule ID	IDE0078
Title	Use pattern matching
Category	Style
Subcategory	Language rules (pattern matching preferences)
Applicable languages	C# 9.0+
Options	`csharp_style_prefer_pattern_matching`

Property	Value
Rule ID	IDE0260
Title	Use pattern matching
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 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)

Property	Value	Description
Option name	csharp_style_prefer_pattern_matching
Option values	`true`	Prefer to use pattern matching constructs, when possible
	`false`	Prefer not to use pattern matching constructs.
Default option value	`true`

csharp_style_pattern_matching_over_as_with_null_check (IDE0260)

This option also configures rule IDE0019.

Property	Value	Description
Option name	csharp_style_pattern_matching_over_as_with_null_check
Option values	`true`	Prefer pattern matching over `as` expression with null-conditional member access.
	`false`	Disables the rule.
Default option value	`true`

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.

ini

[*.{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.

ini

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

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

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