CA1023: Indexers should not be multidimensional

 

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The latest version of this topic can be found at CA1023: Indexers should not be multidimensional.

TypeName|IndexersShouldNotBeMultidimensional|
|CheckId|CA1023|
|Category|Microsoft.Design|
|Breaking Change|Breaking|

A public or protected type contains a public or protected indexer that uses more than one index.

Indexers, that is, indexed properties, should use a single index. Multi-dimensional indexers can significantly reduce the usability of the library. If the design requires multiple indexes, reconsider whether the type represents a logical data store. If not, use a method.

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

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

The following example shows a type, DayOfWeek03, with a multi-dimensional indexer that violates the rule. The indexer can be seen as a type of conversion and therefore is more appropriately exposed as a method. The type is redesigned in RedesignedDayOfWeek03 to satisfy the rule.

using namespace System;

namespace DesignLibrary
{
    public ref class DayOfWeek03
    {
        array<String^, 2>^ dayOfWeek;

    public:
        property String^ default[int,  int]
        {
            String^ get(int month, int day)
            {
                return dayOfWeek[month - 1, day - 1];
            }
        }

        DayOfWeek03()
        {
            dayOfWeek = gcnew array<String^, 2>(12, 7);
            dayOfWeek[0,0] = "Wed";
            dayOfWeek[0,1] = "Thu";
            // ...
            dayOfWeek[1,0] = "Sat";
            dayOfWeek[1,1] = "Sun";
            // ...
        }
    };

    public ref class RedesignedDayOfWeek03
    {
        static array<String^>^ dayOfWeek = 
            {"Tue", "Wed", "Thu", "Fri", "Sat", "Sun", "Mon"};

        static array<int>^ daysInPreviousMonth = 
            {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30};

    public:
        String^ GetDayOfWeek(int month, int day)
        {
            return dayOfWeek[(daysInPreviousMonth[month - 1] + day) % 7];
        }
    };
}

CA1043: Use integral or string argument for indexers

CA1024: Use properties where appropriate

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