Restrictions on Collections & Types

This page lists everything that is currently not supported in T#

T# does not fully support complex C# data types like Dictionary, List<T>, or user-defined script collections.This section lists the type system differences and shows how to work with Terra-compatible collections instead

🧾 Dictionaries

In Unity, Dictionary<TKey, TValue> is used to store and quickly access data using keys — it's a common tool for lookups, mapping, and efficient access patterns. This pattern is not supported in T#.

Dictionary<string, int> myDict = new Dictionary<string, int>();

🔁 What you instead need to do in T# to use key-value pairs: Use TerraDictionary, which is interpreter-compatible.

TerraDictionary myDict = new TerraDictionary();
myDict.Add("key1", 1);

int value = (int)myDict["key1"]; // ✅ Works

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📋 Lists

In Unity, List<T> is the go-to for dynamic arrays — it's used to manage growing or shrinking collections of elements like GameObjects, positions, and more. This approach is not supported in T#.

List<float> myList = new List<float>();
myList.Add(1.5f);
float firstItem = myList[0];

🔁 What you instead need to do in T# to work with dynamic collections: Use TerraList, which works the same way but is compatible with T#.

TerraList myList = new TerraList();
myList.Add(5);
int firstInt = (int)myList[0];

TerraList gameObjectList = new TerraList();
gameObjectList.Add(someGameObject);
GameObject firstObject = (GameObject)gameObjectList[0];

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📦 Structs in TerraList

In Unity, structs are often used for lightweight data containers, and it’s common to store them in collections. This is not supported in T#.

TerraList structList = new TerraList();
structList.Add(new MyStruct()); // ❌

🔁 What you instead need to do in T#: Avoid storing custom structs in TerraList.Only primitive types (like int, float, bool) or supported objects (e.g., GameObject) should be added.

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🧩 Custom Scripts in Collections

In Unity, it's common to store custom script instances inside List<T> or Dictionary<TKey, TValue> for managing multiple game behaviors. This is not supported in T#.

List<MyCustomScript> scriptList = new List<MyCustomScript>();
Dictionary<string, MyCustomScript> scriptDict = new Dictionary<string, MyCustomScript>();

🔁 What you instead need to do in T#: Use GameObject references and access the components as needed.

List<GameObject> objectList = new List<GameObject>();
MyCustomScript script = objectList[0].GetComponent(typeof(MyCustomScript)) as MyCustomScript;

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🧮 LINQ Libraries

Unity developers often use LINQ (.Where(), .ToList(), etc.) for elegant data filtering and querying collections. This is not supported in T#.

var filtered = myList.Where(x => x > 5).ToList();

🔁 What you instead need to do in T#: Use traditional loops to filter or transform data.

List<int> filtered = new List<int>();
for (int i = 0; i < myList.Count; i++) {
    if (myList[i] > 5) {
        filtered.Add(myList[i]);
    }
}