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34 lines
1.7 KiB
Markdown
34 lines
1.7 KiB
Markdown
# Reserve dollar sign (`$`) to be forever unused
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## Summary
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This RFC proposes a stable contract that `$` will not be used for any features in Luau, and will not be accepted as part of identifier tokens.
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## Motivation
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By reserving `$` external pattern matching tools, which at time of writing are already planned to be created by both Roblox and full-moon, can use it to symbolize things like placeholder tokens, similar to [ast-grep](https://ast-grep.github.io/guide/pattern-syntax.html).
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For example, a search in ast-grep for "checking equality to itself" would be `$A == $A`. This becomes ambiguous and harder to write if `$A` is also a valid identifier, or means some potential expression.
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## Design
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Nothing more than a stable contract is necessary. `$` will not be allowed in identifiers, and `$` will not be a component of any syntax being added to the language.
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`$` is chosen as it seems fairly unlikely we will ever use it for any syntax, while at the same time its use as a placeholder token is common.
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- ast-grep, as mentioned before
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- SQL uses `$` for binded parameters in prepared statements
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## Drawbacks
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The dollar sign is used in a couple of places outside Luau:
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- JavaScript, C++, and probably others allow it as an identifier, which jQuery uses as its primary controller
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- PHP, Perl, Bash, and others both use it for variables (`$name = "John"`)
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- Haskell uses it as an infix operator as sugar to help clean up function applications
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These use cases are nowhere near compelling enough to where we would likely do the same.
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## Alternatives
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- Don't do it, as always.
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- Pick a different sigil, though `$` is a fairly clear choice
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