Merge pull request #15270 from dwijnand/same-length

Author: dwijnand

compiler/src/dotty/tools/dotc/core/Decorators.scala

@@ -184,6 +184,9 @@ object Decorators {
       loop(xs, xs, 0)
     end mapWithIndexConserve
 
+    /** True if two lists have the same length.  Since calling length on linear sequences
+     *  is Θ(n), it is an inadvisable way to test length equality.  This method is Θ(n min m).
+     */
     final def hasSameLengthAs[U](ys: List[U]): Boolean = {
       @tailrec def loop(xs: List[T], ys: List[U]): Boolean =
         if (xs.isEmpty) ys.isEmpty

compiler/src/dotty/tools/dotc/core/Denotations.scala

@@ -551,7 +551,7 @@ object Denotations {
           case _ => NoType
       case tp1: PolyType =>
         tp2 match
-          case tp2: PolyType if sameLength(tp1.paramNames, tp2.paramNames) =>
+          case tp2: PolyType if tp1.paramNames.hasSameLengthAs(tp2.paramNames) =>
             val resType = infoMeet(tp1.resType, tp2.resType.subst(tp2, tp1), safeIntersection)
             if resType.exists then
               tp1.derivedLambdaType(

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -1943,7 +1943,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
     case tp1: PolyType =>
       tp2.widen match {
         case tp2: PolyType =>
-          sameLength(tp1.paramNames, tp2.paramNames) &&
+          tp1.paramNames.hasSameLengthAs(tp2.paramNames) &&
           matchesType(tp1.resultType, tp2.resultType.subst(tp2, tp1), relaxed)
         case _ =>
           false

compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala

@@ -286,7 +286,7 @@ trait TypeAssigner {
   def assignType(tree: untpd.Apply, fn: Tree, args: List[Tree])(using Context): Apply = {
     val ownType = fn.tpe.widen match {
       case fntpe: MethodType =>
-        if (sameLength(fntpe.paramInfos, args) || ctx.phase.prev.relaxedTyping)
+        if (fntpe.paramInfos.hasSameLengthAs(args) || ctx.phase.prev.relaxedTyping)
           safeSubstMethodParams(fntpe, args.tpes)
         else
           errorType(i"wrong number of arguments at ${ctx.phase.prev} for $fntpe: ${fn.tpe}, expected: ${fntpe.paramInfos.length}, found: ${args.length}", tree.srcPos)
@@ -358,7 +358,7 @@ trait TypeAssigner {
                 if tp eq pt then pt.newLikeThis(pt.paramNames, pt.paramInfos, pt.resType)
                 else tp)
             val argTypes = args.tpes.mapConserve(ensureFresh)
-            if (sameLength(argTypes, paramNames)) pt.instantiate(argTypes)
+            if (argTypes.hasSameLengthAs(paramNames)) pt.instantiate(argTypes)
             else wrongNumberOfTypeArgs(fn.tpe, pt.typeParams, args, tree.srcPos)
           }
         }
@@ -474,7 +474,7 @@ trait TypeAssigner {
     assert(!hasNamedArg(args) || ctx.reporter.errorsReported, tree)
     val tparams = tycon.tpe.typeParams
     val ownType =
-      if (sameLength(tparams, args))
+      if (tparams.hasSameLengthAs(args))
         if (tycon.symbol == defn.andType) AndType(args(0).tpe, args(1).tpe)
         else if (tycon.symbol == defn.orType) OrType(args(0).tpe, args(1).tpe, soft = false)
         else tycon.tpe.appliedTo(args.tpes)

compiler/src/dotty/tools/package.scala

@@ -8,18 +8,6 @@ package object tools {
 
   val ListOfNil: List[Nil.type] = Nil :: Nil
 
-  /** True if two lists have the same length.  Since calling length on linear sequences
-   *  is O(n), it is an inadvisable way to test length equality.
-   */
-  final def sameLength[T](xs: List[T], ys: List[T]): Boolean = xs match {
-    case _ :: xs1 =>
-      ys match {
-        case _ :: ys1 => sameLength(xs1, ys1)
-        case _ => false
-      }
-    case _ => ys.isEmpty
-  }
-
   /** Throws an `UnsupportedOperationException` with the given method name. */
   def unsupported(methodName: String): Nothing =
     throw new UnsupportedOperationException(methodName)