Language rules

Code-style language rules affect how various constructs of .NET programming languages, for example, modifiers, and parentheses, are used. The rules fall into the following categories:

• .NET style rules: Rules that apply to both C# and Visual Basic. The option names for these rules start with the prefix dotnet_style_.
• C# style rules: Rules that are specific to C# code. The option names for these rules start with the prefix csharp_style_.
• Visual Basic style rules: Rules that are specific to Visual Basic code. The option names for these rules start with the prefix visual_basic_style_.

Option format

Options for language rules can be specified in a configuration file with the following format:

option_name = value (Visual Studio 2019 version 16.9 and later)

or

option_name = value:severity

• Value

  For each language rule, you specify a value that defines if or when to prefer the style. Many rules accept a value of true (prefer this style) or false (do not prefer this style). Other rules accept values such as when_on_single_line or never.

• Severity (optional in Visual Studio 2019 version 16.9 and later versions)

  The second part of the rule specifies the severity level for the rule. When specified in this way, the severity setting is only respected inside development IDEs, such as Visual Studio. It is not respected during build.

  To enforce code style rules at build time, set the severity by using the rule ID-based severity configuration syntax for analyzers instead. The syntax takes the form dotnet_diagnostic.<rule ID>.severity = <severity>, for example, dotnet_diagnostic.IDE0040.severity = none. For more information, see severity level.

.NET style rules

The style rules in this section are applicable to both C# and Visual Basic.

• 'this.' and 'Me.' qualifiers
• Language keywords instead of framework type names for type references
• Modifier preferences
  • Order modifiers (IDE0036)
  • Add accessibility modifiers (IDE0040)
  • Add readonly modifier (IDE0044)
• Parentheses preferences
• Expression-level preferences
  • Use object initializers (IDE0017)
  • Use collection initializers (IDE0028)
  • Use auto-implemented property (IDE0032)
  • Use explicitly provided tuple name (IDE0033)
  • Use inferred member names (IDE0037)
  • Use conditional expression for assignment (IDE0045)
  • Use conditional expression for return (IDE0046)
  • Use compound assignment (IDE0054 and IDE0074)
  • Simplify interpolation (IDE0071)
  • Simplify conditional expression (IDE0075)
  • Add missing cases to switch statement (IDE0010)
  • Convert anonymous type to tuple (IDE0050)
  • Use 'System.HashCode.Combine' (IDE0070)
  • Convert typeof to nameof (IDE0082)
• Null-checking preferences
  • Use coalesce expression (IDE0029 and IDE0030)
  • Use null propagation (IDE0031)
  • Use 'is null' check (IDE0041)
• File header preferences
• Namespace naming preferences (IDE0130)

C# style rules

The style rules in this section are applicable to C# language only.

• 'var' preferences (IDE0007 and IDE0008)
• Expression-bodied members
  • Use expression body for constructors (IDE0021)
  • Use expression body for methods (IDE0022)
  • Use expression body for operators (IDE0023 and IDE0024)
  • Use expression body for properties (IDE0025)
  • Use expression body for indexers (IDE0026)
  • Use expression body for accessors (IDE0027)
  • Use expression body for lambdas (IDE0053)
  • Use expression body for local functions (IDE0061)
• Pattern matching preferences
  • Use pattern matching to avoid 'as' followed by a 'null' check (IDE0019)
  • Use pattern matching to avoid 'is' check followed by a cast (IDE0020 and IDE0038)
  • Use switch expression (IDE0066)
  • Use pattern matching (IDE0078)
  • Use pattern matching (not operator) (IDE0083)
  • Simplify property pattern (IDE0170)
• Expression-level preferences
  • Inline variable declaration (IDE0018)
  • Simplify 'default' expression (IDE0034)
  • Use local function instead of lambda (IDE0039)
  • Deconstruct variable declaration (IDE0042)
  • Use index operator (IDE0056)
  • Use range operator (IDE0057)
  • Simplify new expression (IDE0090)
  • Add missing cases to switch expression (IDE0072)
  • Use tuple to swap values (IDE0180)
• "Null" checking preferences
  • Use throw expression (IDE0016)
  • Use conditional delegate call (IDE1005)
  • Prefer 'null' check over type check (IDE0150)
• Code block preferences
  • Add braces (IDE0011)
  • Use simple 'using' statement (IDE0063)
• 'using' directive preferences (IDE0065)
• Modifier preferences
  • Make local function static (IDE0062)
  • Make struct fields writable (IDE0064)
• Namespace declaration preferences (IDE0160 and IDE0161)

Visual Basic style rules

The style rules in this section are applicable to Visual Basic language only.

• Pattern matching preferences
  • Use pattern matching (IsNot operator) (IDE0084)

See also

• Unnecessary code rules
• Formatting rules
• Naming rules
• .NET code style rules reference