Use pattern matching (IDE0078 and IDE0260)
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 |
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 specify the behavior that you want the rule to enforce. For information about configuring options, see Option format.
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 |
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 |
// 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);
// 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 })
{
}
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.
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