Scala example source code file (FindMembers.scala)

This example Scala source code file (FindMembers.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

boolean, deferred, findmemberbase, list, long, nosymbol, private, reflection, symbol, type, unit

The FindMembers.scala Scala example source code

/* NSC -- new Scala compiler
 * Copyright 2005-2014 LAMP/EPFL
 * @author  Jason Zaugg
 */
package scala.reflect.internal
package tpe

import Flags._
import util.Statistics
import TypesStats._

trait FindMembers {
  this: SymbolTable =>

  /** Implementatation of `Type#{findMember, findMembers}` */
  private[internal] abstract class FindMemberBase[T](tpe: Type, name: Name, excludedFlags: Long, requiredFlags: Long) {
    protected val initBaseClasses: List[Symbol] = tpe.baseClasses

    // The first base class, or the symbol of the ThisType
    // e.g in:
    // trait T { self: C => }
    //
    // The selector class of `T.this.type` is `T`, and *not* the first base class, `C`.
    private[this] var _selectorClass: Symbol = null
    private def selectorClass: Symbol = {
      if (_selectorClass eq null) {
        _selectorClass = tpe match {
          case tt: ThisType => tt.sym // SI-7507 the first base class is not necessarily the selector class.
          case _            => initBaseClasses.head
        }
      }
      _selectorClass
    }

    // Cache for the narrowed type of `tp` (in `tp.findMember`).
    // This is needed to avoid mismatched existential types are reported in SI-5330.
    private[this] var _self: Type = null
    protected def self: Type = {
      // TODO: use narrow only for modules? (correct? efficiency gain?) (<-- Note: this comment predates SI-5330)
      if (_self eq null) _self = narrowForFindMember(tpe)
      _self
    }

    // Main entry point
    def apply(): T = {
      if (Statistics.canEnable) Statistics.incCounter(findMemberCount)
      val start = if (Statistics.canEnable) Statistics.pushTimer(typeOpsStack, findMemberNanos) else null
      try searchConcreteThenDeferred
      finally if (Statistics.canEnable) Statistics.popTimer(typeOpsStack, start)
    }

    protected def result: T

    // SLS 5.1.3 First, a concrete definition always overrides an abstract definition
    private def searchConcreteThenDeferred: T = {
      val deferredSeen = walkBaseClasses(requiredFlags, excludedFlags | DEFERRED)
      if (deferredSeen) // OPT: the `if` avoids a second pass if the first pass didn't spot any candidates.
        walkBaseClasses(requiredFlags | DEFERRED, excludedFlags & ~(DEFERRED.toLong))
      result
    }

    /*
     * Walk up through the decls of each base class.
     *
     * Called in two passes: first excluding deferred, then mandating it.
     *
     * @return if a potential deferred member was seen on the first pass that calls for a second pass,
               and `excluded & DEFERRED != 0L`
     */
    private def walkBaseClasses(required: Long, excluded: Long): Boolean = {
      var bcs = initBaseClasses

      // Have we seen a candidate deferred member?
      var deferredSeen = false

      // All direct parents of refinement classes in the base class sequence
      // from the current `walkBaseClasses`
      var refinementParents: List[Symbol] = Nil

      // Has the current `walkBaseClasses` encountered a non-refinement class?
      var seenFirstNonRefinementClass = false

      val findAll = name == nme.ANYname

      while (!bcs.isEmpty) {
        val currentBaseClass = bcs.head
        val decls = currentBaseClass.info.decls
        var entry = if (findAll) decls.elems else decls.lookupEntry(name)
        while (entry ne null) {
          val sym = entry.sym
          val flags = sym.flags
          val meetsRequirements = (flags & required) == required
          if (meetsRequirements) {
            val excl: Long = flags & excluded
            val isExcluded: Boolean = excl != 0L
            if (!isExcluded && isPotentialMember(sym, flags, currentBaseClass, seenFirstNonRefinementClass, refinementParents)) {
              if (shortCircuit(sym)) return false
              else addMemberIfNew(sym)
            } else if (excl == DEFERRED) {
              deferredSeen = true
            }
          }
          entry = if (findAll) entry.next else decls lookupNextEntry entry
        }

        // SLS 5.2 The private modifier can be used with any definition or declaration in a template.
        //         They are not inherited by subclasses [...]
        if (currentBaseClass.isRefinementClass)
          // SLS 3.2.7 A compound type T1 with . . . with Tn {R } represents objects with members as given in
          //           the component types T1, ..., Tn and the refinement {R }
          //
          //           => private members should be included from T1, ... Tn. (SI-7475)
          refinementParents :::= currentBaseClass.parentSymbols
        else if (currentBaseClass.isClass)
          seenFirstNonRefinementClass = true // only inherit privates of refinement parents after this point

        bcs = bcs.tail
      }
      deferredSeen
    }

    /* Should this symbol be returned immediately as the sole result? */
    protected def shortCircuit(sym: Symbol): Boolean

    /* Add this member to the final result, unless an already-found member matches it. */
    protected def addMemberIfNew(sym: Symbol): Unit

    // Is `sym` a potentially member of `baseClass`?
    //
    // Q. When does a potential member fail to be a an actual member?
    // A. if it is subsumed by an member in a subclass.
    private def isPotentialMember(sym: Symbol, flags: Long, owner: Symbol,
                                  seenFirstNonRefinementClass: Boolean, refinementParents: List[Symbol]): Boolean = {
      // conservatively (performance wise) doing this with flags masks rather than `sym.isPrivate`
      // to avoid multiple calls to `Symbol#flags`.
      val isPrivate      = (flags & PRIVATE) == PRIVATE
      val isPrivateLocal = (flags & PrivateLocal) == PrivateLocal

      // TODO Is the special handling of `private[this]` vs `private` backed up by the spec?
      def admitPrivate(sym: Symbol): Boolean =
        (selectorClass == owner) || (
             !isPrivateLocal // private[this] only a member from within the selector class. (Optimization only? Does the spec back this up?)
          && (
                  !seenFirstNonRefinementClass
               || refinementParents.contains(owner)
             )
        )

      (!isPrivate || admitPrivate(sym)) && (sym.name != nme.CONSTRUCTOR || owner == initBaseClasses.head)
    }

    // True unless the already-found member of type `memberType` matches the candidate symbol `other`.
    protected def isNewMember(member: Symbol, other: Symbol): Boolean =
      (    (other ne member)
        && (    (member.owner eq other.owner)                         // same owner, therefore overload
             || (member.flags & PRIVATE) != 0                         // (unqualified) private members never participate in overriding
             || (other.flags & PRIVATE) != 0                          // ... as overrider or overridee.
             || !(memberTypeLow(member) matches memberTypeHi(other))  // do the member types match? If so, its an override. Otherwise it's an overload.
           )
      )

    // Cache for the member type of a candidate member when comparing against multiple, already-found existing members
    //
    // TODO this cache is probably unnecessary, `tp.memberType(sym: MethodSymbol)` is already cached internally.
    private[this] var _memberTypeHiCache: Type = null
    private[this] var _memberTypeHiCacheSym: Symbol = null

    protected def memberTypeHi(sym: Symbol): Type = {
      if (_memberTypeHiCacheSym ne sym) {
        _memberTypeHiCache = self.memberType(sym)
        _memberTypeHiCacheSym = sym
      }
      _memberTypeHiCache
    }

    // member type of the LHS of `matches` call. This is an extension point to enable a cache in
    // FindMember.
    protected def memberTypeLow(sym: Symbol): Type = self.memberType(sym)

    /** Same as a call to narrow unless existentials are visible
     *  after widening the type. In that case, narrow from the widened
     *  type instead of the proxy. This gives buried existentials a
     *  chance to make peace with the other types. See SI-5330.
     */
    private def narrowForFindMember(tp: Type): Type = {
      val w = tp.widen
      // Only narrow on widened type when we have to -- narrow is expensive unless the target is a singleton type.
      if ((tp ne w) && containsExistential(w)) w.narrow
      else tp.narrow
    }
  }

  private[reflect] final class FindMembers(tpe: Type, excludedFlags: Long, requiredFlags: Long)
    extends FindMemberBase[Scope](tpe, nme.ANYname, excludedFlags, requiredFlags) {
    private[this] var _membersScope: Scope   = null
    private def membersScope: Scope = {
      if (_membersScope eq null) _membersScope = newFindMemberScope
      _membersScope
    }

    protected def shortCircuit(sym: Symbol): Boolean = false
    protected def result: Scope = membersScope

    protected def addMemberIfNew(sym: Symbol): Unit = {
      val members = membersScope
      var others = members.lookupEntry(sym.name)
      var isNew = true
      while ((others ne null) && isNew) {
        val member = others.sym
        if (!isNewMember(member, sym))
          isNew = false
        others = members lookupNextEntry others // next existing member with the same name.
      }
      if (isNew) members.enter(sym)
    }
  }

  private[reflect] final class FindMember(tpe: Type, name: Name, excludedFlags: Long, requiredFlags: Long, stableOnly: Boolean)
    extends FindMemberBase[Symbol](tpe, name, excludedFlags, requiredFlags) {
    // Gathering the results into a hand rolled ListBuffer
    // TODO Try just using a ListBuffer to see if this low-level-ness is worth it.
    private[this] var member0: Symbol       = NoSymbol
    private[this] var members: List[Symbol] = null
    private[this] var lastM: ::[Symbol]     = null

    private def clearAndAddResult(sym: Symbol): Unit = {
      member0 = sym
      members = null
      lastM = null
    }

    protected def shortCircuit(sym: Symbol): Boolean = (name.isTypeName || (stableOnly && sym.isStable && !sym.hasVolatileType)) && {
      clearAndAddResult(sym)
      true
    }

    protected def addMemberIfNew(sym: Symbol): Unit =
      if (member0 eq NoSymbol) {
        member0 = sym // The first found member
      } else if (members eq null) {
        // We've found exactly one member so far...
        if (isNewMember(member0, sym)) {
          // ... make that two.
          lastM = new ::(sym, null)
          members = member0 :: lastM
        }
      } else {
        // Already found 2 or more members
        var ms: List[Symbol] = members

        var isNew = true
        while ((ms ne null) && isNew) {
          val member = ms.head
          if (!isNewMember(member, sym))
            isNew = false
          ms = ms.tail
        }
        if (isNew) {
          val lastM1 = new ::(sym, null)
          lastM.tl = lastM1
          lastM = lastM1
        }
      }

    // Cache for the member type of the first member we find.
    private[this] var _member0Tpe: Type = null
    private[this] def member0Tpe: Type = {
      assert(member0 != null)
      if (_member0Tpe eq null) _member0Tpe = self.memberType(member0)
      _member0Tpe
    }

    override protected def memberTypeLow(sym: Symbol): Type =
      if (sym eq member0) member0Tpe else super.memberTypeLow(sym)

    // Assemble the result from the hand-rolled ListBuffer
    protected def result: Symbol = if (members eq null) {
      if (member0 == NoSymbol) {
        if (Statistics.canEnable) Statistics.incCounter(noMemberCount)
        NoSymbol
      } else member0
    } else {
      if (Statistics.canEnable) Statistics.incCounter(multMemberCount)
      lastM.tl = Nil
      initBaseClasses.head.newOverloaded(tpe, members)
    }
  }
}