Fix #9033, fix #9056: Add EmptyTuple #9049
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nicolasstucki
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We change to the following hierarchy where all generic tuple types erase to `Product`.
```
Product -- Tuple -+- EmptyTuple
|
+- NonEmptyTuple -- *:[Head, Tail <: Tuple]
```
These are encoded using the following compile-time only classes
```scalla
sealed trait Tuple extends Product { ... }
object EmptyTuple extends Tuple { ... }
type EmptyTuple = EmptyTuple.type
sealed trait NonEmptyTuple extends Tuple { ... }
sealed abstract class *:[+H, +T <: Tuple] extends NonEmptyTuple { ... }
```
`TupleN` classes for `1 < N <= 22` are made subtypes of `*:` with precise type (as done before). But `Unit` is not anymore related to `Tuple`.
Construction of empty tuples can be done with `Tuple()`, tuples with one element with `Tuple(e)` while any other tuple are created with `(e1, ..., en)`.
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liufengyun
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| // () | ||
| Literal(Constant(())) | ||
| // scala.EmptyTuple | ||
| ref(defn.EmptyTupleModule.termRef) |
There was a problem hiding this comment.
Maybe define a type in Definitions for defn.EmptyTupleModule.termRef.
odersky
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Jun 8, 2020
|
FWIW, it looks like this PR lead to a 30% slowdown in the "Tuple reverse (Runtime)" benchmark: http://dotty-bench.epfl.ch/ |
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@liufengyun how can I run this benchmark locally? |
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Found it |
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The performance regression comes from the sound type test to fix #9056. We will be able to recover this performance when we brack the API in 3.1 by not erasing https://github.com/lampepfl/dotty/pull/9049/files#diff-69edc152a7680e521f5bfba13aef8220R462 |
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With this PR we change to the following hierarchy where all generic tuple types erase to
Product.These are encoded using the following compile-time only classes
TupleNclasses for1 < N <= 22are made subtypes of*:with precise type (as done before). ButUnitis not anymore related toTuple.Construction of empty tuples can be done with
Tuple(), tuples with one element withTuple(e)while any other tuple are created with(e1, ..., en). These syntactic forms can also be used to match over tuples.Fixes #9033 and fixes #9056.