RFC: or return syntax
#53
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I would really desperately want to see this - my code is littered with places this would be incredible - but a similar idea I mentioned a while back about "return in expressions" got shot down. I really hope there is an expression of this design that can be agreed upon. |
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| ## Summary | ||
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| The `or return` syntax is a more compact, understandable way to end execution if an expression evaluates to `nil`. |
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Inconsistent with usual truthiness test. What if the expression evaluates to false?
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Probably should have clarified here - the main use case is for expressions that can return nil, but the already-established truthiness rules would be respected.
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Would |
| local humanoid = partParent:FindFirstChild("Humanoid") or return | ||
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| humanoid.Health = 0 |
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This is just if local which is proposed in a different RFC, so this isn't a strong motivator.
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if local does also solve this problem, but it also creates a new indentation level which is counter to the goals of this RFC.
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| and compact it into a single, simpler statement: | ||
| ```lua | ||
| local var = foo() or return false |
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Doesn't compose with multrets.
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Why not? As far as I can tell, the only possible reason it wouldn't is if commas were used somewhere else in the expression, which is solved by using a pair of parentheses.
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| `or return` can be implemented as a binary operation with an optional right side, returning `nil` if no value is given. | ||
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| The parsing step would be fairly simple as well. Since the new syntax is a way to express an already-supported feature more concisely, it can be transformed back into its original form in the parser. This means no changes are necessitated on the compiler side. If specified in the middle of an expression, it can temporarily store the value on its left side to perform the nil check, then compute the rest of the expression using the original copy. For example, |
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Parser can't rewrite the AST beyond its local context, so AST changes are required for this feature to work.
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That's understandable. Is there some form of AST expansion/lowering pass that this could fit into, or would this need to be supported in the compiler as well?
I did consider allowing |
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Here's an idea, local humanoid = partParent:FindFirstChild("Humanoid") or else returnIt's never valid Luau to have the And hey, it reads like posh English, that's fun too :) |
A small syntax extension to make handling
nilvalues easier and more concise.Rendered