C# Interfaces

Documentation version: 0.3.6

Define a plain C# interface and implement it on UdonSharpBehaviour classes. Method calls dispatch through the interface — with parameters, return values, properties, multiple implementations, and interface arrays.

public interface INumberOperation
{
    int Apply(int value);
    int LastResult { get; }
}

[UdonBehaviourSyncMode(BehaviourSyncMode.NoVariableSync)]
public class AddNumberOperation : UdonSharpBehaviour, INumberOperation
{
    [SerializeField] private int amount = 5;
    private int _lastResult;

    public int LastResult => _lastResult;

    public int Apply(int value)
    {
        _lastResult = value + amount;
        return _lastResult;
    }
}

Dispatch through the interface:

INumberOperation firstOperation  = addOperation;       // AddNumberOperation
INumberOperation secondOperation = multiplyOperation;  // MultiplyNumberOperation

int added      = firstOperation.Apply(input);   // 10 → 15
int multiplied = secondOperation.Apply(input);  // 10 → 30

Interface field serialization

Unity cannot serialize interface fields. Store the concrete components on your behaviour and assign them to interface locals at runtime (as in the example above).

Interface limitations

Interface support targets the common polymorphism patterns used in worlds:

• Supported: method dispatch with parameters/returns, properties, multiple implementations per class, interface arrays, closed generic interface diamonds.
• Rejected at build time (with diagnostics): constructs outside the supported contract — see Example/GenericRestrictions for the accepted/rejected pairs.

See also

• Extended Language — closed generics and interface diamonds
• Examples — Example/Interfaces runs INumberOperation end to end