CA1002: Do not expose generic lists
| Property | Value |
|---|---|
| Rule ID | CA1002 |
| Title | Do not expose generic lists |
| Category | Design |
| Fix is breaking or non-breaking | Breaking |
| Enabled by default in .NET 9 | No |
Cause
A type contains an externally visible member that is a System.Collections.Generic.List<T> type, returns a List<T> type, or whose signature includes a List<T> parameter.
By default, this rule only looks at externally visible types, but this is configurable.
Rule description
System.Collections.Generic.List<T> is a generic collection that's designed for performance and not inheritance. List<T> does not contain virtual members that make it easier to change the behavior of an inherited class. The following generic collections are designed for inheritance and should be exposed instead of List<T>.
How to fix violations
To fix a violation of this rule, change the System.Collections.Generic.List<T> type to one of the generic collections that's designed for inheritance.
When to suppress warnings
Do not suppress a warning from this rule unless the assembly that raises this warning is not meant to be a reusable library. For example, it would be safe to suppress this warning in a performance-tuned application where a performance benefit was gained from the use of generic lists.
Suppress a warning
If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.
#pragma warning disable CA1002
// The code that's violating the rule is on this line.
#pragma warning restore CA1002
To disable the rule for a file, folder, or project, set its severity to none in the configuration file.
[*.{cs,vb}]
dotnet_diagnostic.CA1002.severity = none
For more information, see How to suppress code analysis warnings.
Configure code to analyze
Use the following option to configure which parts of your codebase to run this rule on.
You can configure this option for just this rule, for all rules it applies to, or for all rules in this category (Design) that it applies to. For more information, see Code quality rule configuration options.
Include specific API surfaces
You can configure which parts of your codebase to run this rule on, based on their accessibility. For example, to specify that the rule should run only against the non-public API surface, add the following key-value pair to an .editorconfig file in your project:
dotnet_code_quality.CAXXXX.api_surface = private, internal
Related rules
CA1005: Avoid excessive parameters on generic types
CA1010: Collections should implement generic interface
CA1000: Do not declare static members on generic types
CA1003: Use generic event handler instances
