Uloop Hot Reload

uloop hot-reload

Replaces method bodies in the running Editor (EditMode or PlayMode) directly from edited project source files — no domain reload, no attributes, no source markers. Private/internal member access, static methods, return values, async methods, and iterators all work within the limits below — including private access inside async, iterator, lambda, local-function, and LINQ-query bodies. Methods that cannot be patched are reported per method as Skipped or Failed; one unpatchable method never aborts the rest of the run.

Usage

uloop hot-reload --files Assets/Scripts/Enemy.cs
uloop hot-reload --files Assets/Scripts/Enemy.cs,Assets/Scripts/Boss.cs
uloop hot-reload
uloop hot-reload --revert-all

Multiple files are passed as one comma-separated value (or a JSON array); array options consume exactly one value token.

A brand-new script — or any script under a brand-new .asmdef — cannot be hot-reloaded before its first import: Unity has not compiled it into any assembly yet. Run uloop compile once to import new files, then iterate on them with hot reload.

Parameters

When --files is omitted or empty, a source is selected only when its compilation assembly has a snapshot directory and that source has its own snapshot file. A missing per-file snapshot is left out rather than guessed as changed, so pass the file explicitly or run uloop compile to establish a complete baseline.

Status

uloop hot-reload --status lists the currently active changes without applying or reverting anything; it cannot be combined with --files or --revert-all. Patches are static Editor state, so after a domain reload it authoritatively reports zero. Each Active row's InvocationCount counts calls into the patched body since the patch was applied — read it as a reachability signal only while the code is actually being driven; interpretation rules are in references/troubleshooting.md.

How It Works

The edited files are grouped by the compiled assembly they belong to. Per group, every editable method body is rewritten into a static shim by an out-of-process Roslyn worker (private/internal access becomes accessor delegates where needed), the shims of the whole group compile into one shim assembly against publicized reference copies and load into the Editor domain, and each original method is patched with a Harmony transpiler (ID io.github.hatayama.uloop.hot-reload). Because a group shares one shim assembly, a body edited in one file can call a method or field added in another edited file of the same assembly. Re-running after a real edit replaces the patch; an unchanged file after a fully applied reload reports AlreadyActive rows and changes nothing, unless another edited file of the same assembly is in the reload — then it is re-applied with that group, and other files of the assembly that hold active patches and are unchanged since they were applied are re-applied too, so every active patch binds to the newest shim. With a compile-time source baseline, only methods whose bodies actually changed are patched (UnchangedTotal counts the rest), and a patched body that matches the baseline again is unpatched on that run.

Scope in Brief

• Patched: ordinary method bodies and property getters with a body.
• Added members: new methods, fields, and supported properties apply as Added rows (see the scope reference for the property shapes still skipped), visible to edited code in the same reload within the same assembly (pass the declaring file and its callers together), and vanish on any compile or domain reload (an Editor-session illusion). New types, references from other assemblies or from files that are neither passed to the reload nor already hot-reloaded, reflection, serialization, and Unity message discovery need uloop compile.
• Signature changes (return type, rename, parameters) follow the added-member rules. A return-type change is gated: it is Skipped unless the same reload — or an earlier one — has patched every live compiled caller of the old signature. A rename or parameter-list change is not gated: it follows the delete rules — the old signature is reported removed, and a Warnings entry names each compiled call site left on the old behavior until uloop compile.
• Constructors, operators, compiled setter/init/indexer accessors, and event accessors are Skipped; finalizers and interface members are silently not applied. const and other outside-body edits never change runtime behavior (drift is warned where detectable).
• A reload applies each file all-or-nothing: any Failed method leaves that file unapplied; patches in other files still apply, except bodies that call an added method whose own shim failed to compile — those are Skipped until it compiles.

Full rules and the Skipped/Failed condition tables: references/scope-and-limits.md.

Workflow

Treat hot reload as the exploration phase and uloop compile as the landing phase: keep edits inside the edited files, collect structural changes, and compile once — every compile drops all patches and pause points and resets the PlayMode session (the compile response's Warning states how many were live). While patches are active, AutoRefreshHeld is true so returning focus does not recompile; uloop compile or --revert-all releases the hold. One-shot methods (Awake, Start, initialization helpers) patch successfully but show no effect on the call that already ran; the response marks them with LifecycleNote. For values you expect to tune while playing, expose a static property getter instead of a const.

Reference Guides

All files live in references/ beside this skill; read the one whose trigger matches:

• references/scope-and-limits.md — full scope rules: added members, signature changes, Skipped/Failed tables, source baselines, one-shot code, tunable getters.
• references/mechanism-and-lifecycle.md — patch mechanism, convergence, what survives which reload, Editor-code iteration without PlayMode.
• references/troubleshooting.md — Patched but no behavior change, JIT inlining, reading --status and InvocationCount.
• references/pause-point-interaction.md — how patches re-target or suppress armed pause points; one-way reachability checks.
• references/output.md — every response field: ErrorCode, NextActions, Methods rows, Warnings, totals.