Hotloading — live code reloading, IL fast path, and common pitfalls

Hotloading — Live Code Reloading

s&box recompiles and live-reloads your assembly whenever you save a .cs or .razor file. You don't need to restart the editor for most changes.

How It Works

Diagnosing Slow Hotloads

Run hotload_log 2 in the console to get a timing breakdown of which types are taking longest to process. If instance counts grow each hotload, you likely have a static list that's never cleared.

Pitfalls (Full Hotload Only)

Removing or Renaming Types

References to removed types become null. Renamed types are treated as removed — the old type disappears and the new one starts fresh. Restart the editor if you get cascading errors after a rename.

Changing Default Field Values

Runtime values are copied into the new assembly, so changing a field's default won't take effect until editor restart. Use a property with a => body or const to work around this:

// ❌ Won't update on hotload
public static string Name = "Old";

// ✔️ Always reflects the new value
public static string Name => "New";
public const string Name = "New";

// ✔️ Force skip — uses new default
[SkipHotload] public static string Name = "New";

Static Fields in Generic Types

Static fields in generic types (MyClass<T>) are not processed during hotload — their values are lost. The compiler emits a warning for these. Suppress with [SkipHotload] if intentional.

Delegates and Lambdas

Hotload tries to preserve delegate instances but may fail if lambda methods are reordered or significantly changed. A failed delegate logs a warning when invoked.

Reflection Caches

If you cache reflection results, mark the cache field with [SkipHotload] and repopulate it after hotload to avoid stale data.

Dictionaries / HashSets

If a code change makes previously non-equal instances equal, dictionaries and sets can enter an invalid state. A warning is emitted and an editor restart may be needed.

Performance Tips

• Seal classes that don't need inheritance — hotload can skip them automatically
• Use struct arrays of value types — they have a fast path
• Avoid large static collections that grow unboundedly