CA1043: Use integral or string argument for indexers

TypeName

UseIntegralOrStringArgumentForIndexers

CheckId

CA1043

Category

Microsoft.Design

Breaking Change

Breaking

Cause

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

Rule Description

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.

How to Fix Violations

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

When to Suppress Warnings

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

Example

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
using System;

namespace DesignLibrary
{
    public class Months
    {
        string[] month = new string[] {"Jan", "Feb", "..."};

        public string this[int index]
        {
            get
            {
                return month[index];
            }
        }
    }
}
using namespace System;

namespace DesignLibrary
{
    public ref class Months
    {
        array<String^>^ month;

    public:
        property String^ default[int]
        {
           String^ get(int index)
           {
              return month[index];
           }
           void set(int index, String^ value)
           {
              month[index] = value;
           }
        }

        Months()
        {
            month = gcnew array<String^>(12);
            month[0] = "Jan";
            month[1] = "Feb";
            //...;
        }
    };
}

CA1023: Indexers should not be multidimensional

CA1024: Use properties where appropriate