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057a18573a
Implements the new `module` header syntax as described in "module and package changes" [1]: ``` module [Request, Response, req] ``` The old syntax should still work fine, and is automatically upgraded to the new one when running `roc format`. [1] https://docs.google.com/document/d/1E_77fO-44BtoBtXoVeWyGh1xN2KRTWTu8q6i25RNNx0/edit
29 lines
966 B
Text
29 lines
966 B
Text
## Most users won't need Box, it is used for:
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## - Holding unknown Roc types when developing [platforms](https://github.com/roc-lang/roc/wiki/Roc-concepts-explained#platform).
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## - To improve performance in rare cases.
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##
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module [box, unbox]
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## Allocates a value on the heap. Boxing is an expensive process as it copies
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## the value from the stack to the heap. This may provide a performance
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## optimization for advanced use cases with large values. A platform may require
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## that some values are boxed.
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## ```roc
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## expect Box.unbox (Box.box "Stack Faster") == "Stack Faster"
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## ```
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box : a -> Box a
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## Returns a boxed value.
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## ```roc
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## expect Box.unbox (Box.box "Stack Faster") == "Stack Faster"
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## ```
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unbox : Box a -> a
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# # we'd need reset/reuse for box for this to be efficient
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# # that is currently not implemented
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# map : Box a, (a -> b) -> Box b
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# map = \boxed, transform =
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# boxed
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# |> Box.unbox
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# |> transform
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# |> Box.box
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