Simplify LINQ type check and cast (IDE0121)

Overview

This rule flags LINQ expressions where the type of elements of a sequence are checked (by calling Where<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)) and then cast to that type (by calling either Cast<TResult>(IEnumerable) or Select<TSource,TResult>(IEnumerable<TSource>, Func<TSource,TResult>)). The code fixer converts these expressions to call OfType<TResult>(IEnumerable) instead.

Options

This rule has no associated code-style options.

Example

// Code with violations.
IEnumerable<int> y = objects.Where(a => a is int).Cast<int>();
IEnumerable<int> z = objects.Where(a => a is int).Select(a => (int)a);

// Fixed code.
IEnumerable<int> y = objects.OfType<int>();
IEnumerable<int> z = objects.OfType<int>();

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 IDE0121
// The code that's violating the rule is on this line.
#pragma warning restore IDE0121

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

[*.{cs,vb}]
dotnet_diagnostic.IDE0121.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

• Language rules
• Code style rules reference