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Remove unnecessary lambda expression (IDE0200)

  • Article
Property Value
Rule ID IDE0200
Title Remove unnecessary lambda expression
Category Style
Subcategory Language rules (code-block preferences)
Applicable languages C# 11+
Options csharp_style_prefer_method_group_conversion

Overview

This rule flags the use of a lambda expression where it's unnecessary. Lambda expressions might be unnecessary when the following are all true:

  • The expression includes a method invocation.
  • The lambda expression has the same number and order of parameters as the method invocation.
  • The method invocation has no side effects.
  • The lambda expression isn't assigned to a non-delegate type.
  • If the invocation is a generic method, the type arguments are supplied.
  • The invoked method's return type can be converted to the lambda expression's return type.
  • There's only one applicable method in the method group.

Options

Options specify the behavior that you want the rule to enforce. For information about configuring options, see Option format.

csharp_style_prefer_method_group_conversion

Property Value Description
Option name csharp_style_prefer_method_group_conversion
Option values true Prefer to convert a lambda expression to a method group.
false Disables the rule.
Default option value true

Example

// Code with violations.
bool IsEven(int x) => x % 2 == 0;
_ = new[] { 1, 2, 3 }.Where(n => IsEven(n));

// Fixed code.
bool IsEven(int x) => x % 2 == 0;
_ = new[] { 1, 2, 3 }.Where(IsEven);

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 IDE0200
// The code that's violating the rule is on this line.
#pragma warning restore IDE0200

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

[*.{cs,vb}]
dotnet_diagnostic.IDE0200.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