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Use integral or string argument for indexers

TypeName

UseIntegralOrStringArgumentForIndexers

CheckId

CA1043

Category

Microsoft.Design

Breaking Change

Breaking

A public or protected type contains a public or protected indexer that uses an index type other than System.Int32, System.Int64, System.Object, or System.String.

Indexers, that is, indexed properties, should use integer or string types for the index. These types are typically used for indexing data structures and increase the usability of the library. Use of the Object type should be restricted to those cases where the specific integer or string type cannot be specified at design time. If the design requires other types for the index, reconsider whether the type represents a logical data store. If it does not represent a logical data store, use a method.

To fix a violation of this rule, change the index to an integer or string type, or use a method instead of the indexer.

Exclude a warning from this rule only after carefully considering the need for the nonstandard indexer.

The following example shows an indexer that uses an Int32 index.

Imports System

Namespace DesignLibrary

    Public Class Months

        Private month() As String = {"Jan", "Feb", "..."}

        Default ReadOnly Property Item(index As Integer) As String
            Get
                Return month(index)
            End Get
        End Property

    End Class

End Namespace

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