diff options
Diffstat (limited to 'src')
-rw-r--r-- | src/compiler/scala/tools/nsc/transform/Constructors.scala | 128 |
1 files changed, 85 insertions, 43 deletions
diff --git a/src/compiler/scala/tools/nsc/transform/Constructors.scala b/src/compiler/scala/tools/nsc/transform/Constructors.scala index 31990917f5..cbfcc2cc58 100644 --- a/src/compiler/scala/tools/nsc/transform/Constructors.scala +++ b/src/compiler/scala/tools/nsc/transform/Constructors.scala @@ -10,6 +10,9 @@ import scala.collection.mutable.ListBuffer import symtab.Flags._ import util.TreeSet +/** This phase converts classes with parameters into Java-like classes with + * fields, which are assigned to from constructors. + */ abstract class Constructors extends Transform { import global._ import definitions._ @@ -24,12 +27,14 @@ abstract class Constructors extends Transform { class ConstructorTransformer extends Transformer { def transformClassTemplate(impl: Template): Template = { - val clazz = impl.symbol.owner - val stats = impl.body + val clazz = impl.symbol.owner // the transformed class + val stats = impl.body // the transformed template body val localTyper = typer.atOwner(impl, clazz) - var constr: DefDef = null - var constrParams: List[Symbol] = null - var constrBody: Block = null + + var constr: DefDef = null // The primary constructor + var constrParams: List[Symbol] = null // ... and its parameters + var constrBody: Block = null // ... and its body + // decompose primary constructor into the three entities above. for (stat <- stats) { stat match { @@ -44,11 +49,15 @@ abstract class Constructors extends Transform { } assert((constr ne null) && (constrBody ne null), impl) + // The parameter accessor fields which are members of the class val paramAccessors = clazz.constrParamAccessors + // The constructor parameter corresponding to an accessor def parameter(acc: Symbol): Symbol = parameterNamed(nme.getterName(acc.originalName)) + // The constructor parameter with given name. This means the parameter + // has given name, or starts with given name, and continues with a `$' afterwards. def parameterNamed(name: Name): Symbol = { def matchesName(param: Symbol) = param.name == name || @@ -60,9 +69,12 @@ abstract class Constructors extends Transform { var thisRefSeen: Boolean = false + // A transformer for expressions that go into the constructor val intoConstructorTransformer = new Transformer { override def transform(tree: Tree): Tree = tree match { case Apply(Select(This(_), _), List()) => + // references to parameter accessor methods of own class become references to parameters + // outer accessors become references to $outer parameter if ((tree.symbol hasFlag PARAMACCESSOR) && tree.symbol.owner == clazz) gen.mkAttributedIdent(parameter(tree.symbol.accessed)) setPos tree.pos else if (tree.symbol.outerSource == clazz && !clazz.isImplClass) @@ -71,6 +83,7 @@ abstract class Constructors extends Transform { super.transform(tree) case Select(This(_), _) if ((tree.symbol hasFlag PARAMACCESSOR) && !tree.symbol.isSetter && tree.symbol.owner == clazz) => + // references to parameter accessor field of own class become references to parameters gen.mkAttributedIdent(parameter(tree.symbol)) setPos tree.pos case Select(_, _) => thisRefSeen = true @@ -86,62 +99,76 @@ abstract class Constructors extends Transform { } } + // Move tree into constructor, take care of changing owner from `oldowner' to constructor symbol def intoConstructor(oldowner: Symbol, tree: Tree) = intoConstructorTransformer.transform( new ChangeOwnerTraverser(oldowner, constr.symbol)(tree)) + // Should tree be moved in front of super constructor call? def canBeMoved(tree: Tree) = tree match { //todo: eliminate thisRefSeen case ValDef(mods, _, _, _) => (mods hasFlag PRESUPER | PARAMACCESSOR) || !thisRefSeen case _ => false } + // Create an assignment to class field `to' with rhs `from' def mkAssign(to: Symbol, from: Tree): Tree = - atPos(to.pos) { - localTyper.typed { + localTyper.typed { + atPos(to.pos) { Assign(Select(This(clazz), to), from) } } + // Create code to copy parameter to parameter accessor field. + // If parameter is $outer, check that it is not null. def copyParam(to: Symbol, from: Symbol): Tree = { var result = mkAssign(to, Ident(from)) if (from.name == nme.OUTER) result = atPos(to.pos) { localTyper.typed { - If(Apply(Select(Ident(from), nme.eq), List(Literal(Constant(null)))), - Throw(New(TypeTree(NullPointerExceptionClass.tpe), List(List()))), - result); + If( + Apply( + Select(Ident(from), nme.eq), + List(Literal(Constant(null)))), + Throw(New(TypeTree(NullPointerExceptionClass.tpe), List(List()))), + result) } } result } + // The list of definitions that go into class val defBuf = new ListBuffer[Tree] + + // The list of statements that go into constructor after superclass constructor call val constrStatBuf = new ListBuffer[Tree] + + // The list of statements that go into constructor before superclass constructor call val constrPrefixBuf = new ListBuffer[Tree] + + // The early initialized field definitions of the class (these are the class members) val presupers = treeInfo.preSuperFields(stats) + + // generate code to copy pre-initialized fields for (stat <- constrBody.stats) { constrStatBuf += stat stat match { case ValDef(mods, name, _, _) if (mods hasFlag PRESUPER) => - constrStatBuf += - localTyper.typed { - atPos(stat.pos) { - val fields = presupers filter ( - vdef => nme.localToGetter(vdef.name) == name) - assert(fields.length == 1) - Assign( - gen.mkAttributedRef(clazz.thisType, fields.head.symbol), - Ident(stat.symbol)) - } - } + // stat is the constructor-local definition of the field value + val fields = presupers filter ( + vdef => nme.localToGetter(vdef.name) == name) + assert(fields.length == 1) + constrStatBuf += mkAssign(fields.head.symbol, Ident(stat.symbol)) case _ => } } + // Triage all template definitions to go into defBuf, constrStatBuf, or constrPrefixBuf. for (stat <- stats) stat match { case DefDef(mods, name, tparams, vparamss, tpt, rhs) => + // methods with constant result type get literals as their body + // all methods except the primary constructor go into template stat.symbol.tpe match { case MethodType(List(), tp @ ConstantType(c)) => defBuf += copy.DefDef( @@ -151,39 +178,50 @@ abstract class Constructors extends Transform { if (!stat.symbol.isPrimaryConstructor) defBuf += stat } case ValDef(mods, name, tpt, rhs) => + // val defs with constant right-hand sides are eliminated. + // for all other val defs, an empty valdef goes into the template and + // the initializer goes as an assignment into th constructor + // if the val def is an early initialized or a parameter accessor, it goes + // before the superclass constructor call, otherwise it goes after. if (!stat.symbol.tpe.isInstanceOf[ConstantType]) { - try { if (rhs != EmptyTree && !stat.symbol.hasFlag(LAZY)) { val rhs1 = intoConstructor(stat.symbol, rhs); (if (canBeMoved(stat)) constrPrefixBuf else constrStatBuf) += mkAssign( stat.symbol, rhs1) } defBuf += copy.ValDef(stat, mods, name, tpt, EmptyTree) - } catch { - case ex: Throwable => - println("error when transforming "+stat+" in "+stats) - throw ex - } } case ClassDef(_, _, _, _) => + // classes are treated recursively, and left in the template defBuf += (new ConstructorTransformer).transform(stat) case _ => + // all other statements go into the constructor constrStatBuf += intoConstructor(impl.symbol, stat) } + // ----------- avoid making fields for symbols that are not accessed -------------- + + // A sorted set of symbols that are known to be accessed outside the primary constructor. val accessedSyms = new TreeSet[Symbol]((x, y) => x isLess y) - /** list of outer accessor symbols and their bodies */ + // a list of outer accessor symbols and their bodies var outerAccessors: List[(Symbol, Tree)] = List() - /** Is symbol known to be accessed outside of the primary constructor, - * or is it a symbol whose definition cannot be omitted anyway? */ - def isAccessed(sym: Symbol) = - sym.owner != clazz || - !((sym hasFlag PARAMACCESSOR) && sym.isPrivateLocal || - sym.isOuterAccessor && sym.owner == clazz && sym.owner.isFinal && sym.allOverriddenSymbols.isEmpty) || - (accessedSyms contains sym) + // Could symbol's definition be omitted, provided it is not accessed? + // This is the case if the symbol is defined in the current class, and + // ( the symbol is an object private parameter accessor field, or + // the symbol is an outer accessor of a final class which does not override another outer accesser. ) + def maybeOmittable(sym: Symbol) = + (sym.owner == clazz && + ((sym hasFlag PARAMACCESSOR) && sym.isPrivateLocal || + sym.isOuterAccessor && sym.owner.isFinal && sym.allOverriddenSymbols.isEmpty)) + + // Is symbol known to be accessed outside of the primary constructor, + // or is it a symbol whose definition cannot be omitted anyway? + def mustbeKept(sym: Symbol) = + !maybeOmittable(sym) || (accessedSyms contains sym) + // A traverser to set accessedSyms and outerAccessors val accessTraverser = new Traverser { override def traverse(tree: Tree) = { tree match { @@ -191,7 +229,7 @@ abstract class Constructors extends Transform { if (tree.symbol.isOuterAccessor && tree.symbol.owner == clazz && clazz.isFinal) => outerAccessors ::= (tree.symbol, body) case Select(_, _) => - if (!isAccessed(tree.symbol)) accessedSyms addEntry tree.symbol + if (!mustbeKept(tree.symbol)) accessedSyms addEntry tree.symbol super.traverse(tree) case _ => super.traverse(tree) @@ -199,19 +237,21 @@ abstract class Constructors extends Transform { } } - // first traverse all definitions except outeraccesors - // (outeraccessors are avoided in accessTraverser) + // first traverse all definitions except outeraccesors + // (outeraccessors are avoided in accessTraverser) for (stat <- defBuf.elements) accessTraverser.traverse(stat) // then traverse all bodies of outeraccessors which are accessed themselves // note: this relies on the fact that an outer accessor never calls another // outer accessor in the same class. for ((accSym, accBody) <- outerAccessors) - if (isAccessed(accSym)) accessTraverser.traverse(accBody) + if (mustbeKept(accSym)) accessTraverser.traverse(accBody) - val paramInits = for (acc <- paramAccessors if isAccessed(acc)) + // Initialize all parameters fields that must be kept. + val paramInits = for (acc <- paramAccessors if mustbeKept(acc)) yield copyParam(acc, parameter(acc)) + // Assemble final constructor defBuf += copy.DefDef( constr, constr.mods, constr.name, constr.tparams, constr.vparamss, constr.tpt, copy.Block( @@ -219,12 +259,14 @@ abstract class Constructors extends Transform { paramInits ::: constrPrefixBuf.toList ::: constrStatBuf.toList, constrBody.expr)); + // Unlink all fields that can be dropped from class scope for (sym <- clazz.info.decls.toList) - if (!isAccessed(sym)) clazz.info.decls unlink sym + if (!mustbeKept(sym)) clazz.info.decls unlink sym + // Eliminate all field definitions that can be dropped from template copy.Template(impl, impl.parents, impl.self, - defBuf.toList filter (stat => isAccessed(stat.symbol))) - } + defBuf.toList filter (stat => mustbeKept(stat.symbol))) + } // transformClassTemplate override def transform(tree: Tree): Tree = tree match { |