Extension Indexer

An Extension Indexer can refer to a few different concepts depending on your programming language or context. Most notably, it refers to C# 14’s extension indexers feature and Visual Basic’s XML extension indexer property. 1. C# 14 Extension Indexers

In C# 14, Microsoft introduced Extension Members, which drastically upgraded traditional extension methods. For years, you could only attach new methods to an existing type that you didn’t own. With C# 14, you can now add extension indexers (along with extension properties and operators).

Syntax: Instead of creating a messy static class, you use a dedicated extension block.

Use Case: This allows you to treat an external type or a standard collection as an array using the [] square bracket notation. For example, you can write an extension indexer on a standard string to make it a line-addressable source without wrapping it in a custom class.

// Example of C# 14 Extension Indexer syntax public extension MyStringExtension target string { public char this[int index] => this[index]; // Custom indexing rules } Use code with caution. 2. Visual Basic XML Extension Indexer

In Visual Basic, the Extension Indexer Property has existed for a long time. It is explicitly used to access individual elements within an XML collection.

How it Works: When you use an XML axis property (like getting a collection of child elements), you use the extension indexer to pick a specific node.

Safety Feature: The VB compiler translates this into a call to ElementAtOrDefault. If your specified index is out of bounds, it returns Nothing instead of crashing with an exception. This is highly useful when parsing XML feeds where the number of elements is dynamic and unpredictable. 3. Azure AI Search Indexers

If you are working in cloud data architecture, you might hear “extension indexer” informally when talking about extending Azure AI Search Indexers. Extension Indexer Property – Visual Basic | Microsoft Learn