From 944e677f437c39d85280c388cab000b5490e4386 Mon Sep 17 00:00:00 2001 From: Olivier Blanvillain Date: Thu, 6 Apr 2017 18:35:20 +0200 Subject: Decouple Product and pattern-matching Product pattern use to: - have a `<: Product` requirement - compute the arity of a pattern by looking at `N` in a `ProductN` superclass. This commit changes `<: Product`, instead we look for a `_1` member. The arity is determined by inspecting `_1` to `_N` members instead. --- Here another attempt to formalize Dotty's pattern-matching (base on #1805). This covers the *Extractor Patterns* [section of the spec](https://www.scala-lang.org/files/archive/spec/2.12/08-pattern-matching.html#extractor-patterns). Dotty support 4 different extractor patterns: Boolean Pattern, Product Pattern, Seq Pattern and Name Based Pattern. Boolean Pattern - Extractor defines `def unapply(x: T): Boolean` - Pattern-matching on exactly `0` patterns Product Pattern - Extractor defines `def unapply(x: T): U` - `N > 0` is the maximum number of consecutive (parameterless `def` or `val`) `_1: P1` ... `_N: PN` members in `U` - Pattern-matching on exactly `N` patterns with types `P1, P2, ..., PN` Seq Pattern - Extractor defines `def unapplySeq(x: T): U` - `U` has (parameterless `def` or `val`) members `isEmpty: Boolean` and `get: S` - `S <: Seq[V]` - Pattern-matching on any number of pattern with types `V, V, ..., V` Name Based Pattern - Extractor defines `def unapply(x: T): U` - `U` has (parameterless `def` or `val`) members `isEmpty: Boolean` and `get: S` - If there is exactly `1` pattern, pattern-matching on `1` pattern with type `S` - Otherwise fallback to Product Pattern on type `U` In case of ambiguities, *Product Pattern* is preferred over *Name Based Pattern*. --- compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala') diff --git a/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala b/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala index dbc7666f7..519767389 100644 --- a/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala +++ b/compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala @@ -233,7 +233,7 @@ class PatternMatcher extends MiniPhaseTransform with DenotTransformer { // next: MatchMonad[U] // returns MatchMonad[U] def flatMap(prev: Tree, b: Symbol, next: Tree): Tree = { - val resultArity = defn.productArity(b.info) + val resultArity = productArity(b.info) if (isProductMatch(prev.tpe, resultArity)) { val nullCheck: Tree = prev.select(defn.Object_ne).appliedTo(Literal(Constant(null))) ifThenElseZero( -- cgit v1.2.3