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🚀 C# Indexers – Enable Array-Like Access to Custom Objects

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🧲 Introduction – Why Use Indexers in C#?

Sometimes you want your object to behave like an array or collection—allowing access to its internal elements using square brackets. Indexers in C# let you do exactly that. They allow objects to be indexed like arrays, improving usability, abstraction, and code readability.

🎯 In this guide, you’ll learn:

• What indexers are and how they work
• How to define and use indexers in C#
• Real-world use cases and syntax patterns
• Best practices and tips for implementation

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🔍 Core Concept – What Is an Indexer?

An indexer allows an object of a class or struct to be accessed using an index, similar to an array. It is defined using the this keyword and square brackets [].

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🔣 Basic Syntax of an Indexer

class Sample
{
    private string[] names = new string[3];

    public string this[int index]
    {
        get => names[index];
        set => names[index] = value;
    }
}

📘 this[int index] allows the object to be indexed like sample[0].

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💻 Code Example – Using an Indexer

Sample s = new Sample();
s[0] = "Alice";
s[1] = "Bob";

Console.WriteLine(s[0]); // Output: Alice

🧵 Explanation:

• s[0] = "Alice"; calls the indexer’s set
• Console.WriteLine(s[0]); calls the indexer’s get

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🧩 Indexer with Multiple Parameters

class Matrix
{
    private int[,] data = new int[3, 3];

    public int this[int row, int col]
    {
        get => data[row, col];
        set => data[row, col] = value;
    }
}

📘 Access like:

Matrix m = new Matrix();
m[0, 1] = 5;
Console.WriteLine(m[0, 1]); // Output: 5

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🧠 Indexer vs Property

Feature	Property	Indexer
Access Pattern	obj.PropertyName	obj[index]
Use Case	Named data member	Indexed collection-like access
Supports Multiple Params	❌ Typically no	✅ Yes

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🛠️ Real-World Use Cases

• 📦 Custom collections (e.g., MyList<T>)
• 🗂️ Representing matrix or grid data
• 🧾 Wrappers over Dictionary<TKey, TValue>
• 🧪 Table row/column mappings
• 📋 Form field access via keys

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💡 Best Practices & Tips

💡 Tip: Validate the index to avoid IndexOutOfRangeException.

⚠️ Pitfall: Don’t use indexers for actions with side effects—it should only access or modify internal data.

📘 Best Practice: Combine indexers with internal collections like arrays or lists.

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📌 Summary – Recap & Next Steps

🧵 Key Takeaways:

• Indexers allow custom objects to be indexed like arrays.
• Use this[index] to define readable and writable access.
• Support multiple parameters for 2D structures.

⚙️ Real-world relevance: Widely used in custom data containers, matrix structures, and collection wrappers in C#.

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❓ FAQ Section

❓ Can a class have more than one indexer?
✅ No. A class can only have one indexer, but it can be overloaded with different parameter types.

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❓ Can indexers be overloaded?
✅ Yes. You can define multiple indexers with different parameter types or counts.

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❓ Can I use string as an index?
✅ Yes. Indexers support any type as an index:

public string this[string key] { get; set; }

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❓ Do indexers support access modifiers?
✅ Yes. You can define separate access levels for get and set.

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❓ Are indexers the same as arrays?
✅ No. Indexers just mimic array syntax but are custom-defined. Arrays are built-in types.

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