luau/rfcs/read-only-environment.md

Read-Only Environment

Summary

Add _ENV as a safe alternative to getfenv.

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 read-only global table _ENV with clones of all base functions and libraries.

Drawbacks

Roblox's marketplace currently hides assets that use getfenv so it would need to be updated to hide assets with _ENV.