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Cristian Sifuentes
Cristian Sifuentes

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Implicit Index Access in C# 13 — Using `^` in Object Initializers

#csharp #dotnet #indexing #programming

ImplicitIndexAccessInCSharp13

Implicit Index Access in C# 13 — Using ^ in Object Initializers

The ^ operator (read as "from the end") has been part of C# since version 8, allowing developers to easily access elements from the end of collections:

int last = myArray[^1]; // Last element
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However, until C# 13, you couldn’t use ^ inside object initializers. This restriction has now been lifted, giving developers more expressive and compact ways to initialize collections directly.

Let’s explore how this change improves array initialization syntax and simplifies common patterns.

What Changed in C# 13?

Prior to C# 13:

var countdown = new TimerRemaining(); countdown.buffer[^1] = 0; // Valid
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But you could not write:

var countdown = new TimerRemaining { buffer = { [^1] = 0 } // ❌ Compiler error before C# 13 };
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Now, this syntax is fully supported.

C# 13: Using ^ in Initializers 

public class TimerRemaining { public int[] buffer { get; set; } = new int[10]; } var countdown = new TimerRemaining() { buffer = { [^1] = 0, [^2] = 1, [^3] = 2, [^4] = 3, [^5] = 4, [^6] = 5, [^7] = 6, [^8] = 7, [^9] = 8, [^10] = 9 } };
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This initializes the array in reverse order using "from the end" indexing:

Index Expression Actual Index Value
[^1] 9 0
[^2] 8 1
... ... ...
[^10] 0 9

Why It Matters

Benefit Description
Expressive and clean No need to calculate exact indices manually
Improved readability Shows intent clearly in object initializer
Enables reverse logic patterns Useful in countdowns, buffers, stack-like data
Supports all IList<T>-like APIs Works with arrays, lists, spans, etc.

Real-World Scenarios

Buffer Initialization for Reverse Countdown 

class Timer { public int[] buffer = new int[5]; } var timer = new Timer { buffer = { [^1] = 0, [^2] = 1, [^3] = 2, [^4] = 3, [^5] = 4 } };
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Visual Debugging Benefit

When using [^] indexing in initializers, debuggers show clearly mapped reverse values — making this great for pre-populating data in predictable orders.

Things to Keep in Mind

Caution Details
Only supported in C# 13+ Will not compile in earlier versions
Requires IList<T>-style collection Not valid for custom index-only properties
Index out of range is still a risk ^6 on a 5-element array will throw

Learn More

Final Thoughts

This small C# 13 enhancement brings a powerful touch of expressiveness and clarity to object initializers — especially when initializing arrays in reverse or mirrored patterns.

The addition of implicit ^ indexing inside object initializers helps make C# smarter, terser, and more readable.

Use it where logic demands intuitive backwards indexing — and let your intent shine through.

Written by: [Cristian Sifuentes] – C# Syntax Explorer | Modern Patterns Advocate | Fluent API Enthusiast

Do you use ^ indexing in production? This change might clean up your code even more.

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