'var' preferences (IDE0007 and IDE0008)

Article
10/20/2022

This article describes two related rules, IDE0007 and IDE0008.

Property	Value
Rule ID	IDE0007
Title	Use `var` instead of explicit type
Category	Style
Subcategory	Language rules ('var' preferences)
Applicable languages	C#
Options	`csharp_style_var_for_built_in_types`
	`csharp_style_var_when_type_is_apparent`
	`csharp_style_var_elsewhere`

Property	Value
Rule ID	IDE0008
Title	Use explicit type instead of `var`
Category	Style
Subcategory	Language rules ('var' preferences)
Applicable languages	C#
Options	`csharp_style_var_for_built_in_types`
	`csharp_style_var_when_type_is_apparent`
	`csharp_style_var_elsewhere`

Overview

These two style rules define whether the var keyword or an explicit type should be used in a variable declaration. To enforce that var is used, set the severity of IDE0007 to warning or error. To enforce that the explicit type is used, set the severity of IDE0008 to warning or error.

Options

This rule's associated options define where this style preference should be applied:

Built-in types (csharp_style_var_for_built_in_types)
Places where the type is apparent (csharp_style_var_when_type_is_apparent)
Elsewhere (csharp_style_var_elsewhere)

For more information about configuring options, see Option format.

csharp_style_var_for_built_in_types

Property	Value	Description
Option name	csharp_style_var_for_built_in_types
Option values	`true`	Prefer `var` is used to declare variables with built-in system types such as `int`
	`false`	Prefer explicit type over `var` to declare variables with built-in system types such as `int`
Default option value	`false`

// csharp_style_var_for_built_in_types = true
var x = 5;

// csharp_style_var_for_built_in_types = false
int x = 5;

csharp_style_var_when_type_is_apparent

Property	Value	Description
Option name	csharp_style_var_when_type_is_apparent
Option values	`true`	Prefer `var` when the type is already mentioned on the right-hand side of a declaration expression
	`false`	Prefer explicit type when the type is already mentioned on the right-hand side of a declaration expression
Default option value	`false`

// csharp_style_var_when_type_is_apparent = true
var obj = new Customer();

// csharp_style_var_when_type_is_apparent = false
Customer obj = new Customer();

csharp_style_var_elsewhere

Property	Value	Description
Option name	csharp_style_var_elsewhere
Option values	`true`	Prefer `var` over explicit type in all cases, unless overridden by another code style rule
	`false`	Prefer explicit type over `var` in all cases, unless overridden by another code style rule
Default option value	`false`

// csharp_style_var_elsewhere = true
var f = this.Init();

// csharp_style_var_elsewhere = false
bool f = this.Init();

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 IDE0007 // Or IDE0008
// The code that's violating the rule is on this line.
#pragma warning restore IDE0007 // Or IDE0008

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

[*.{cs,vb}]
dotnet_diagnostic.IDE0007.severity = none
dotnet_diagnostic.IDE0008.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.