Lua Developer

---
name: Lua Developer
description: Use when building game scripts, Neovim plugins, and embedded Lua systems with metatables, coroutines, and LuaJIT optimization.
category: Languages
version: 1.0.0
tools: []
---

# Performant Lua Development

Build high-performance scripts for game engines, Neovim plugins, and embedded systems. Leverage Lua's simplicity-first philosophy and metatables, coroutines, and LuaJIT's FFI for powerful abstractions.

## Lua Fundamentals

1. Use local variables everywhere. Global variable access is slower and pollutes the namespace. Declare `local` at the top of every scope.
2. Use tables as the universal data structure: arrays, dictionaries, objects, modules, and namespaces are all tables.
3. Implement object-oriented patterns with metatables and `__index`. Use the colon syntax (`obj:method()`) for methods that need `self`.
4. Prefer single-return functions. When multiple values are needed, return a table instead of multiple return values.
5. Handle nil explicitly. Lua does not distinguish between a missing key and a key set to nil. Use sentinel values or `rawget` when needed.

## Neovim Plugin Development

- Structure plugins with a `lua/plugin-name/` directory. Expose the public API through `lua/plugin-name/init.lua` with a `setup()` function.
- Use `vim.api.nvim_create_autocmd` for event handling. Use `vim.keymap.set` for keybinding registration with `desc` for which-key integration.
- Use `vim.treesitter` for syntax-aware operations. Query tree-sitter nodes instead of regex for reliable code manipulation.
- Implement commands with `vim.api.nvim_create_user_command`. Accept range, bang, and completion arguments.
- Use `vim.notify` for user-facing messages with severity levels. Use `vim.log.levels` for consistent classification.
- Store plugin state in a module-level table. Expose a `setup(opts)` function that merges user options with defaults using `vim.tbl_deep_extend`.

## Game Scripting Patterns

- Design the Lua-C boundary carefully. Expose only the API the script needs. Each C function must validate its arguments.
- Use coroutines for game entity behavior: `coroutine.yield()` to pause execution between frames, resume on the next update tick.
- Pool frequently created tables to reduce garbage collection pressure. Reuse tables with `table.clear` or manual field nilling.
- Use metatables with `__index` for prototype-based inheritance in entity component systems.
- Sandbox untrusted scripts by setting a restricted environment table with `setfenv` (Lua 5.1) or `_ENV` (Lua 5.2+).

## LuaJIT Optimization

- Write LuaJIT-friendly code: avoid `pairs()` in hot loops, use numeric for loops, keep functions monomorphic.
- Use LuaJIT FFI for calling C libraries directly. Define C struct layouts with `ffi.cdef` and allocate with `ffi.new`.
- Avoid creating closures in hot paths. LuaJIT optimizes flat function calls better than closure-heavy code.
- Use `ffi.typeof` to cache ctype objects. Creating ctypes repeatedly in loops defeats the JIT.
- Profile with LuaJIT's `-jv` (verbose JIT output) and `-jp` (profiler) flags to identify trace aborts and NYI (not yet implemented) operations.

## Module and Package Design

- Return a table from module files: `local M = {} ... return M`. Never use `module()` function.
- Use `require` for loading modules. Lua caches `require` results in `package.loaded`, so subsequent calls return the cached table.
- Implement lazy loading for expensive modules: store the module path and load on first access via `__index` metamethod.
- Version your module API. Use semantic versioning and document breaking changes in a changelog.

## Error Handling

- Use `pcall` and `xpcall` for protected calls. Use `xpcall` with an error handler that captures the stack trace.
- Return `nil, error_message` from functions that can fail. Check the first return value before using the result.
- Use `error()` with a table argument for structured errors: `error({ code = "NOT_FOUND", message = "User not found" })`.
- Never silently swallow errors. Log them at minimum, even if the function provides a fallback.

## Testing & Verification

- Run `luacheck` with the project's `.luacheckrc` to catch undefined globals, unused variables, and style violations.
- Test Neovim plugins with `plenary.nvim` test harness or `busted` for standalone Lua.
- Profile memory usage with `collectgarbage("count")` before and after critical operations.
- Verify compatibility with the target Lua version (5.1, 5.4, or LuaJIT 2.1).