Resolving the Issue of Immutable State in C# Structs: A Guide to Using Classes Instead

Struggling with member variables losing their assigned values in Unity? Discover why structs may not be the best choice and how to easily switch to classes for better state management in your game development projects.
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Resolving the Issue of Immutable State in C- Structs: A Guide to Using Classes Instead

When you're developing a game in Unity, managing the states of various screens and their children is an essential part of the user experience. However, programmers occasionally encounter perplexing issues with state management, particularly when using structs in C-. A common problem arises when a member variable seemingly loses its assigned value after a function call, leaving developers scratching their heads. In this post, we'll explore this issue in detail and present a clear solution that involves reconsidering how we structure our ScreenState.

Understanding the Problem

In your code, you have designed a ScreenState struct that contains a reference to child states stored in a dictionary. You expect the child state to change correctly when invoking the ChangeChildState method. However, you notice that the value of _currentChild does not persist beyond the scope of that function. Although you're changing it within the function, the change does not reflect in the original struct stored in your _states dictionary.

This issue arises from the fundamental differences between value types and reference types in C-. Let's unpack this.

What is a Struct?

In C-, a struct is a value type. Each time you pass a struct, such as when you retrieve it from a dictionary, a new copy is created. This means modifying this copy does not affect the original struct stored in the collection.

The Symptoms

After calling ChangeChildState, the _currentChild retains the value "BazarBuyBug" indefinitely.

The child state does not correctly switch to "BazarBuyFurniture", as expected.

The Solution: Switch to Classes or Update Struct Usage

To resolve this issue, we have two primary paths:

Option 1: Convert Structs to Classes

The simplest and most effective solution to this problem is to change your ScreenState from a struct to a class. Doing so will allow the ScreenState to be a reference type, meaning when you pass it around, you won't create unnecessary copies. Here's a brief overview of what you need to do:

Change Struct to Class: Change your declaration from struct ScreenState to class ScreenState.

Update References: Ensure that any instantiation reflects this change (e.g., new ScreenState(...) remains the same).

Option 2: Keep Structs and Modify Code

If you prefer to keep the ScreenState as a struct due to specific design decisions or requirements, you need to correctly manage the changes to _currentChild. Here's how to update your code:

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This ensures that any changes made to the struct within the method are reflected back to the dictionary.

Conclusion

Understanding the differences between structs and classes in C- is critical for effective state management in your Unity projects. By recognizing the limitations of value types and making the necessary adjustments, you can ensure that your game states behave as expected. Whether you choose to switch to classes or adapt your use of structs, being aware of these nuances will empower you to create more robust and interactive game experiences.

Now that you're equipped with this knowledge, go ahead and revisit your ScreenState implementation. Happy coding!