1.4 KiB
Read-Only Environment
Summary
Add a way to access a read-only version of the environment without disabling safeenv.
Motivation
There are valid use cases for accessing the environment in a read-only way. As defined in the RFC for deprecating getfenv and setfenv there are outlined cases where reading the environment is useful.
Increased performance can be achieved for transpilers written in Luau that may not be able to have a static environment created to access functions from or cant directly transpile 1:1. Similarly interpreters written in Luau can benefit from being able to access functions without deoptimization, making other optimizations still active.
Design
A safe way to access the environment is with a read-only table with __index and __iter metamethods.
a) _ENV table
A read-only global table with metamethods that point to LUA_ENVIRONINDEX.
b) getenv or getrenv function
Works identically to getfenv but only provides read-only access to the function's environment.
Drawbacks
Type-checking can be difficult.
Roblox's marketplace currently hides assets that use getfenv so it would need to be updated to hide assets with _ENV/getenv/getrenv.
Environments can have metamethods of their own which may not interface well with a read-only getenv/getrenv.