Do not expose generic lists

Cause

A type contains an externally visible member that is a System.Collections.Generic.List<T> type, returns a System.Collections.Generic.List<T> type, or whose signature includes a System.Collections.Generic.List<T> parameter.

Rule Description

System.Collections.Generic.List<T> is a generic collection designed for performance not inheritance. System.Collections.Generic.List<T> does not contain virtual members that make it easier to implement new behaviors. The following generic collections are designed for inheritance and should be exposed instead of System.Collections.Generic.List<T>.

• System.Collections.ObjectModel.Collection<T>

• System.Collections.ObjectModel.ReadOnlyCollection<T>

• System.Collections.ObjectModel.KeyedCollection<TKey, TItem>

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 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.

Related Rules

Avoid excessive parameters on generic types

Collections should implement generic interface

Do not declare static members on generic types

Do not nest generic types in member signatures

Generic methods should provide type parameter

Use generic event handler instances

Use generics where appropriate

See Also

Reference

Generics (C# Programming Guide)