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