Indexers

Let’s go through indexers in C# — a feature that makes objects behave like arrays.

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📌 1. What is an Indexer?

• An indexer allows an object of a class or struct to be accessed using array-like syntax (obj[index]).

• Essentially, it defines how the object responds to the [] operator.

• Useful when your class wraps a collection or you want custom access logic.

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📌 2. Syntax of an Indexer

public class SampleCollection
{
    private string[] data = new string[5];
 
    // Indexer
    public string this[int index]
    {
        get { return data[index]; }
        set { data[index] = value; }
    }
}

• this[int index] → defines the indexer

• get → called when accessing obj[index]

• set → called when assigning obj[index] = value

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📌 3. Example Usage

SampleCollection collection = new SampleCollection();
 
// Using indexer like an array
collection[0] = "Hello";
collection[1] = "World";
 
Console.WriteLine(collection[0]); // Hello
Console.WriteLine(collection[1]); // World

• Notice how collection[0] behaves like a normal array, but the logic is defined in your class.

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📌 4. Key Points

1. Indexers can be overloaded with different parameter types (int, string, etc.)

2. No name is needed for an indexer; it’s always this[...]

3. Can be read-write, read-only, or write-only depending on which accessors you implement

Example: String-based Indexer

public string this[string key]
{
    get { return data[Array.IndexOf(data, key)]; }
}

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📌 5. Analogy

• Think of an indexer as a custom array:

  • Your object acts like an array

  • You can control how data is stored or retrieved

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📌 6. Benefits

• Encapsulates internal data structures

• Provides array-like access to objects without exposing the underlying collection

• Supports custom logic when getting or setting values

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✅ Tip:

• Use indexers when your class represents a collection or needs array-like access with custom logic.

• They are often used in wrappers around dictionaries, lists, or custom data structures.

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