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Synchronous Exception Handling

Documentation version: 0.3.6

Compiler-managed try/catch/finally with explicit throws, rethrow, and guarded null, index, and integral divide/modulo failures — without relying on unavailable Udon exception opcodes.

try
{
    LoadSlot(selectedIndex);
}
catch (ArgumentException exception)
{
    Debug.LogError(exception.Message);
}
catch (UdonException exception)
{
    Debug.LogError(exception.Operation + ": " + exception.Message);
}
finally
{
    isBusy = false;
}

What is guarded​

The compiler recognizes explicit throw new statements and guards:

  • null receivers,
  • array/string indices,
  • integral division or modulo,

inside protected code and its same-behaviour call graph.

UdonException carries Kind, Code, Operation, and Message; standard catch variables expose only Message. Catch-all clauses and throw; are supported, and all abrupt exits run applicable finally blocks.

:::caution Synchronous emulation This is synchronous emulation. A real fault raised inside an Udon extern cannot be intercepted and still halts that behaviour. Custom events, network calls, other behaviours, floating-point division, overflow, casts, and SDK domain failures are exception boundaries or outside v1. :::

await inside try is rejected with a targeted diagnostic; existing asynchronous callback/result behavior is unchanged. See ExceptionHandlingExample.cs.

See also​