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Use coalesce expression (IDE0029 and IDE0030)

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This article describes two related rules, IDE0029 and IDE0030.

Property Value
Rule ID IDE0029
Title Use coalesce expression (non-nullable types)
Category Style
Subcategory Language rules (null-checking preferences)
Applicable languages C# and Visual Basic
Options dotnet_style_coalesce_expression
Property Value
Rule ID IDE0030
Title Use coalesce expression (nullable types)
Category Style
Subcategory Language rules (null-checking preferences)
Applicable languages C# and Visual Basic
Options dotnet_style_coalesce_expression

Overview

These style rules concern the use of null-coalescing expressions, for example, x ?? y, versus ternary conditional expressions with null checks, for example, x != null ? x : y. The two related rule IDs differ with respect to the nullability of the expressions:

  • IDE0029: Used when non-nullable expressions are involved. For example, this rule could recommend x ?? y instead of x != null ? x : y when x and y are non-nullable reference types.
  • IDE0030: Used when nullable expressions are involved. For example, this rule could recommend x ?? y instead of x != null ? x : y when x and y are nullable value types or nullable reference types.

Options

Set the value of the associated option to specify whether null-coalescing expressions or ternary operator checking is preferred. The rule enforces whichever option you choose.

For more information about configuring options, see Option format.

dotnet_style_coalesce_expression

Property Value Description
Option name dotnet_style_coalesce_expression
Option values true Prefer null coalescing expressions to ternary operator checking
false Prefer ternary operator checking to null coalescing expressions
Default option value true 
// dotnet_style_coalesce_expression = true
var v = x ?? y;

// dotnet_style_coalesce_expression = false
var v = x != null ? x : y; // or
var v = x == null ? y : x;

' dotnet_style_coalesce_expression = true
Dim v = If(x, y)

' dotnet_style_coalesce_expression = false
Dim v = If(x Is Nothing, y, x) ' or
Dim v = If(x IsNot Nothing, x, y)

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 IDE0029 // Or IDE0030
// The code that's violating the rule is on this line.
#pragma warning restore IDE0029 // Or IDE0030

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

[*.{cs,vb}]
dotnet_diagnostic.IDE0029.severity = none
dotnet_diagnostic.IDE0030.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