This article describes two related rules,IDE0020 andIDE0038.

Overview

This style rule concerns the use of C#pattern matching, for example,o is int i, over anis check followed by a cast, for example,if (o is int) { ... (int)o ... }. Enable eitherIDE0020 orIDE0038 based on whether or not the cast expression should be saved into a separate local variable:

• IDE0020: Cast expressionis saved into a local variable. For example,if (o is int) { var i = (int)o; } saves the result of(int)o in a local variable.
• IDE0038: Cast expressionis not saved into a local variable. For example,if (o is int) { if ((int)o == 1) { ... } } does not save the result of(int)o into a local variable.

Options

Set the value of the associated option for this rule to specify whether pattern matching oris check followed by a type cast is preferred.

For more information about configuring options, seeOption format.

csharp_style_pattern_matching_over_is_with_cast_check

// csharp_style_pattern_matching_over_is_with_cast_check = trueif (o is int i) {...}// csharp_style_pattern_matching_over_is_with_cast_check = falseif (o is int) {var i = (int)o; ... }

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 IDE0020 // Or IDE0038// The code that's violating the rule is on this line.#pragma warning restore IDE0020 // Or IDE0038

To disable the rule for a file, folder, or project, set its severity tonone in theconfiguration file.

[*.{cs,vb}]dotnet_diagnostic.IDE0020.severity = nonedotnet_diagnostic.IDE0038.severity = none

To disable all of the code-style rules, set the severity for the categoryStyle tonone in theconfiguration file.

[*.{cs,vb}]dotnet_analyzer_diagnostic.category-Style.severity = none

For more information, seeHow to suppress code analysis warnings.

See also

• Pattern matching in C#
• Code style language rules
• Code style rules reference