diff options
author | Martin Odersky <odersky@gmail.com> | 2007-04-30 22:56:06 +0000 |
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committer | Martin Odersky <odersky@gmail.com> | 2007-04-30 22:56:06 +0000 |
commit | 03f09f244ec0ce9fc3891a8eaab0a4024fae7d87 (patch) | |
tree | aa20e0555b2e1dd9260cf1c13cd5eaa9ed96ff4d | |
parent | 750e57765b10d0f072eff68274047daa1c2040ae (diff) | |
download | scala-03f09f244ec0ce9fc3891a8eaab0a4024fae7d87.tar.gz scala-03f09f244ec0ce9fc3891a8eaab0a4024fae7d87.tar.bz2 scala-03f09f244ec0ce9fc3891a8eaab0a4024fae7d87.zip |
added support for notnull, first steps
8 files changed, 135 insertions, 83 deletions
diff --git a/src/compiler/scala/tools/nsc/ast/TreeGen.scala b/src/compiler/scala/tools/nsc/ast/TreeGen.scala index ff3b2a21d6..2baea3f4e2 100644 --- a/src/compiler/scala/tools/nsc/ast/TreeGen.scala +++ b/src/compiler/scala/tools/nsc/ast/TreeGen.scala @@ -156,6 +156,11 @@ abstract class TreeGen { def mkAsInstanceOf(value: Tree, tpe: Type): Tree = mkAsInstanceOf(value, tpe, global.phase.erasedTypes) + def mkCheckInit(tree: Tree): Tree = + if (tree.hasSymbol && tree.symbol.tpe <:< NotNullClass.tpe && !tree.symbol.tpe.isNotNull) + mkRuntimeCall(nme.checkInitialized, List(tree)) + else tree + /** Builds a list with given head and tail. */ def mkNewCons(head: Tree, tail: Tree): Tree = New(Apply(mkAttributedRef(definitions.ConsClass), List(head, tail))) diff --git a/src/compiler/scala/tools/nsc/symtab/Definitions.scala b/src/compiler/scala/tools/nsc/symtab/Definitions.scala index 1c898082bc..67404caf12 100644 --- a/src/compiler/scala/tools/nsc/symtab/Definitions.scala +++ b/src/compiler/scala/tools/nsc/symtab/Definitions.scala @@ -106,6 +106,7 @@ trait Definitions { def SeqFactory = getMember(ScalaRunTimeModule, nme.Seq); def checkDefinedMethod = getMember(ScalaRunTimeModule, "checkDefined") def isArrayMethod = getMember(ScalaRunTimeModule, "isArray") + var NotNullClass: Symbol = _ var BoxesUtilityModule: Symbol = _ var ComparatorModule: Symbol = _ def Comparator_equals = getMember(ComparatorModule, nme.equals_) @@ -873,6 +874,7 @@ trait Definitions { getClass(if (forMSIL) "System.IndexOutOfRangeException" else "java.lang.IndexOutOfBoundsException") ScalaRunTimeModule = getModule("scala.runtime.ScalaRunTime") + NotNullClass = getClass("scala.NotNull") BoxesUtilityModule = getModule("scala.runtime.BoxesUtility") ComparatorModule = getModule("scala.runtime.Comparator") RepeatedParamClass = newCovariantPolyClass( diff --git a/src/compiler/scala/tools/nsc/symtab/StdNames.scala b/src/compiler/scala/tools/nsc/symtab/StdNames.scala index 5afe99bed0..fd1893054c 100644 --- a/src/compiler/scala/tools/nsc/symtab/StdNames.scala +++ b/src/compiler/scala/tools/nsc/symtab/StdNames.scala @@ -247,7 +247,7 @@ trait StdNames { val booleanValue = newTermName("booleanValue") val box = newTermName("box") val boxArray = newTermName("boxArray") - val checkCastability = newTermName("checkCastability") + val checkInitialized = newTermName("checkInitialized") val classOf = newTermName("classOf") val coerce = newTermName("coerce") val defaultValue = newTermName("defaultValue") diff --git a/src/compiler/scala/tools/nsc/symtab/Types.scala b/src/compiler/scala/tools/nsc/symtab/Types.scala index 5e62b50f23..a1015eed4a 100644 --- a/src/compiler/scala/tools/nsc/symtab/Types.scala +++ b/src/compiler/scala/tools/nsc/symtab/Types.scala @@ -63,6 +63,55 @@ trait Types { */ var intersectionWitness = new HashMap[List[Type], Type] + /** A proxy for a type (identified by field `tp') that forwards all operations to it + * Every operation that is overridden for some kind of types should be forwarded. + */ + trait TypeProxy extends Type { + val tp: Type + + private def maybeRewrap(newtp: Type) = if (newtp eq tp) this else newtp + + // the following are all operations in class Type that are overridden in some subclass + // Important to keep this up-to-date when new operations are added! + override def isTrivial = tp.isTrivial + override def symbol = tp.symbol + override def singleDeref = maybeRewrap(tp.singleDeref) + override def widen = maybeRewrap(tp.widen) + override def deconst = maybeRewrap(tp.deconst) + override def typeOfThis = tp.typeOfThis + override def narrow = tp.narrow + override def bounds = tp.bounds + override def parents = tp.parents + override def prefix = tp.prefix + override def typeArgs = tp.typeArgs + override def resultType = maybeRewrap(tp.resultType) + override def finalResultType = maybeRewrap(tp.finalResultType) + override def paramSectionCount = tp.paramSectionCount + override def paramTypes = tp.paramTypes + override def typeParams = tp.typeParams + override def notNull = maybeRewrap(tp.notNull) + override def instantiateTypeParams(formals: List[Symbol], actuals: List[Type]) = + tp.instantiateTypeParams(formals, actuals) + override def isHigherKinded: boolean = tp.isHigherKinded + override def normalize = maybeRewrap(tp.normalize) + override def isError = tp.isError + override def isErroneous = tp.isErroneous + override def isStable: boolean = tp.isStable + override def isNotNull = tp.isNotNull + override def decls = tp.decls + override def baseType(clazz: Symbol) = tp.baseType(clazz) + override def closure = tp.closure + override def closureDepth = tp.closureDepth + override def baseClasses = tp.baseClasses + override def cloneInfo(owner: Symbol) = maybeRewrap(tp.cloneInfo(owner)) + override def prefixString = tp.prefixString + override def isComplete = tp.isComplete + override def complete(sym: Symbol) = tp.complete(sym) + override def load(sym: Symbol): unit = tp.load(sym) + override def withAttributes(attribs: List[AnnotationInfo[Any]]) = tp.withAttributes(attribs) + override def withoutAttributes = tp.withoutAttributes + } + /** The base class for all types */ abstract class Type { @@ -85,9 +134,13 @@ trait Types { * identity for all other types */ def widen: Type = this + /** Map a constant type or not-null-type to its underlying base type, + * identity for all other types */ + def deconst: Type = this + /** The type of <code>this</code> of a class type or reference type */ - def typeOfThis = symbol.typeOfThis + def typeOfThis: Type = symbol.typeOfThis /** Map to a this type which is a subtype of this type. */ @@ -95,10 +148,6 @@ trait Types { if (phase.erasedTypes) this else refinedType(List(this), commonOwner(this), EmptyScope).narrow - /** Map a constant type to its underlying base type, - * identity for all other types */ - def deconst: Type = this - /** For a TypeBounds type, itself; * for a reference denoting an abstract type, its bounds, * for all other types, a TypeBounds type all of whose bounds are this type. @@ -137,6 +186,10 @@ trait Types { * the empty list for all other types */ def typeParams: List[Symbol] = List() + /** Mixin a NotNull trait unless type already has one */ + def notNull: Type = + if (isNotNull) this else NotNullType(this) + /** Replace formal type parameter symbols with actual type arguments. * * Amounts to substitution except for higher-kinded types. (See overridden method in TypeRef) -- @M (contact adriaan.moors at cs.kuleuven.be) @@ -162,12 +215,12 @@ trait Types { /** Does this type denote a stable reference (i.e. singleton type)? */ def isStable: boolean = false + /** Is this type guaranteed not to have `null' as a value? */ + def isNotNull: boolean = false + /** Does this type denote a reference type which can be null? */ // def isNullable: boolean = false - /** Is this type guaranteed to be non-null? */ - // def isNonNull: boolean = false - /** For a classtype or refined type, its defined or declared members; * inherited by subtypes and typerefs. * The empty scope for all other types */ @@ -549,7 +602,14 @@ trait Types { override def closure: Array[Type] = supertype.closure override def closureDepth: int = supertype.closureDepth override def baseClasses: List[Symbol] = supertype.baseClasses - // override def isNonNull = supertype.isNonNull + override def isNotNull = supertype.isNotNull + } + + case class NotNullType(tp: Type) extends SubType with TypeProxy { + override def supertype = tp + override def isNotNull: boolean = true + override def deconst: Type = tp + override def toString(): String = supertype.toString() + " with NotNull" } /** A base class for types that represent a single value @@ -618,7 +678,7 @@ trait Types { case class ThisType(sym: Symbol) extends SingletonType { //assert(sym.isClass && !sym.isModuleClass || sym.isRoot, sym) override def isTrivial: boolean = sym.isPackageClass - // override def isNonNull = true + override def isNotNull = true override def symbol = sym override def singleDeref: Type = sym.typeOfThis override def prefixString = @@ -641,7 +701,7 @@ trait Types { case class SingleType(pre: Type, sym: Symbol) extends SingletonType { override val isTrivial: boolean = pre.isTrivial // override def isNullable = supertype.isNullable - // override def isNonNull = supertype.isNonNull + override def isNotNull = supertype.isNotNull private var singleDerefCache: Type = _ private var singleDerefPeriod = NoPeriod override def singleDeref: Type = { @@ -677,7 +737,7 @@ trait Types { case class SuperType(thistpe: Type, supertp: Type) extends SingletonType { override val isTrivial: boolean = thistpe.isTrivial && supertp.isTrivial - // override def isNonNull = true; + override def isNotNull = true; override def symbol = thistpe.symbol override def singleDeref = supertp override def prefix: Type = supertp.prefix @@ -860,7 +920,7 @@ trait Types { symbol.thisType } - // override def isNonNull: boolean = parents forall (.isNonNull); + override def isNotNull: boolean = parents exists (.isNotNull) // override def isNullable: boolean = // parents forall (p => p.isNullable && !p.symbol.isAbstractType); @@ -1025,8 +1085,11 @@ trait Types { case class ConstantType(value: Constant) extends SingletonType { assert(value.tpe.symbol != UnitClass) override def isTrivial: boolean = true + override def isNotNull = value.value != null override def symbol: Symbol = value.tpe.symbol - override def singleDeref: Type = value.tpe //M@ probably ok since constants don't take type params? + override def singleDeref: Type = + if (value.value.isInstanceOf[String]) value.tpe + else value.tpe override def deconst: Type = value.tpe override def toString(): String = value.tpe.toString() + "(" + value.escapedStringValue + ")" @@ -1320,7 +1383,7 @@ A type's symbol should never be inspected directly. * to the core compiler, but can be observed by type-system plugins. The * core compiler does take care to propagate attributes and to save them * in the symbol tables of object files. */ - case class AnnotatedType(attributes: List[AnnotationInfo[Any]], tp: Type) extends Type { + case class AnnotatedType(attributes: List[AnnotationInfo[Any]], tp: Type) extends TypeProxy { override def toString(): String = { val attString = if (attributes.isEmpty) @@ -1339,20 +1402,7 @@ A type's symbol should never be inspected directly. /** Remove any attributes from this type */ override def withoutAttributes = tp.withoutAttributes - override def isTrivial: boolean = tp.isTrivial - - /** Return the argument, unless it is eq to tp, in which case return the - * receiver. This method is used for methods like singleDeref and widen, - * so that the attributes are remembered more frequently. */ - private def maybeRewrap(newtp: Type) = - if (newtp eq tp) this else newtp - - // ---------------- methods forwarded to tp ------------------ \\ - - override def symbol: Symbol = tp.symbol - override def singleDeref: Type = maybeRewrap(tp.singleDeref) - override def widen: Type = maybeRewrap(tp.widen) - override def deconst: Type = maybeRewrap(tp.deconst) + /** Martin to Lex: I don't understand what the following 2 method do? */ override def bounds: TypeBounds = { val oftp = tp.bounds oftp match { @@ -1360,17 +1410,6 @@ A type's symbol should never be inspected directly. case _ => oftp } } - override def parents: List[Type] = tp.parents - override def prefix: Type = tp.prefix - override def typeArgs: List[Type] = tp.typeArgs - override def resultType: Type = maybeRewrap(tp.resultType) - override def finalResultType: Type = maybeRewrap(tp.finalResultType) - override def paramSectionCount: int = tp.paramSectionCount - override def paramTypes: List[Type] = tp.paramTypes - override def typeParams: List[Symbol] = tp.typeParams - override def isStable: boolean = tp.isStable - override def nonPrivateDecl(name: Name): Symbol = tp.nonPrivateDecl(name) - override def baseType(clazz: Symbol): Type = tp.baseType(clazz) override def closure: Array[Type] = { val oftp = tp.closure if ((oftp.length == 1 &&) (oftp(0) eq this)) @@ -1378,14 +1417,6 @@ A type's symbol should never be inspected directly. else oftp } - override def closureDepth: int = tp.closureDepth - override def baseClasses: List[Symbol] = tp.baseClasses - override def cloneInfo(owner: Symbol) = maybeRewrap(cloneInfo(owner)) - override def isComplete: boolean = tp.isComplete - override def complete(sym: Symbol) = tp.complete(sym) - override def load(sym: Symbol): unit = tp.load(sym) - override def findMember(name: Name, excludedFlags: int, requiredFlags: long, stableOnly: boolean): Symbol = - tp.findMember(name, excludedFlags, requiredFlags, stableOnly) } /** A class representing an as-yet unevaluated type. @@ -1750,12 +1781,14 @@ A type's symbol should never be inspected directly. case TypeVar(_, constr) => if (constr.inst != NoType) this(constr.inst) else tp + case NotNullType(tp) => + val tp1 = this(tp) + if (tp1 eq tp) tp + else NotNullType(tp1) case AnnotatedType(attribs, atp) => val atp1 = this(atp) - if (atp1 eq atp) - tp - else - AnnotatedType(attribs, atp1) + if (atp1 eq atp) tp + else AnnotatedType(attribs, atp1) case _ => tp // throw new Error("mapOver inapplicable for " + tp); @@ -2105,6 +2138,7 @@ A type's symbol should never be inspected directly. case MethodType(_, _) => mapOver(tp) case TypeVar(_, _) => mapOver(tp) case AnnotatedType(_,_) => mapOver(tp) + case NotNullType(_) => mapOver(tp) case _ => tp } } @@ -2290,7 +2324,10 @@ A type's symbol should never be inspected directly. } finally { pendingSubTypes -= p } - } else isSubType0(tp1, tp2) + } else { + isSubType0(tp1, tp2) + } + } finally { stc = stc - 1 } @@ -2322,7 +2359,9 @@ A type's symbol should never be inspected directly. case (SingleType(_, _), SingleType(_, _)) => tp1 =:= tp2 case (ConstantType(_), ConstantType(_)) => tp1 =:= tp2 - case (TypeRef(pre1, sym1, args1), TypeRef(pre2, sym2, args2)) if !(tp1.isHigherKinded || tp2.isHigherKinded) => //Console.println("isSubType " + tp1 + " " + tp2);//DEBUG + case (TypeRef(pre1, sym1, args1), TypeRef(pre2, sym2, args2)) + if !(tp1.isHigherKinded || tp2.isHigherKinded) => + //Console.println("isSubType " + tp1 + " " + tp2);//DEBUG if (inIDE) { trackTypeIDE(sym1); trackTypeIDE(sym2); } def isSubArgs(tps1: List[Type], tps2: List[Type], @@ -2342,15 +2381,14 @@ A type's symbol should never be inspected directly. || sym2.isAbstractType && !(tp2 =:= tp2.bounds.lo) && (tp1 <:< tp2.bounds.lo) || -// sym2 == NonNullClass && tp1.isNonNull -// || - sym2.isClass && - ({ val base = tp1 baseType sym2; !(base eq tp1) && (base <:< tp2) }) + sym2.isClass && + ({ val base = tp1 baseType sym2; !(base eq tp1) && (base <:< tp2) }) || - sym1 == AllClass + sym1 == AllClass || // Console.println("last chance " + sym1 + " " + sym2 + " " + sym2.isClass + " " (sym2 isSubClass ObjectClass)) - sym1 == AllRefClass && sym2.isClass && sym2 != AllClass && (sym2 isSubClass ObjectClass)) + sym1 == AllRefClass && + sym2.isClass && (sym2 isNonBottomSubClass ObjectClass) && (!(tp2.normalize.symbol isNonBottomSubClass NotNullClass))) case (MethodType(pts1, res1), MethodType(pts2, res2)) => (pts1.length == pts2.length && matchingParams(pts1, pts2, tp2.isInstanceOf[JavaMethodType]) && @@ -2377,16 +2415,21 @@ A type's symbol should never be inspected directly. atp1 <:< tp2 case (_, AnnotatedType(_,atp2)) => tp1 <:< atp2 + case (NotNullType(ntp1), _) => + ntp1 <:< tp2 + case (_, NotNullType(ntp2)) => + tp1.isNotNull && tp1 <:< ntp2 case (_, _) if (tp1.isHigherKinded || tp2.isHigherKinded) => - (tp1.symbol == AllClass + (tp1.symbol == AllClass || - tp2.symbol == AnyClass // @M Any and Nothing are super-type resp. subtype of every well-kinded type + tp2.symbol == AnyClass // @M Any and Nothing are super-type resp. subtype of every well-kinded type || // @M! normalize reduces higher-kinded case to PolyType's - (tp1.isHigherKinded && tp2.isHigherKinded) && isSubType0(tp1.normalize, tp2.normalize)) + (tp1.isHigherKinded && tp2.isHigherKinded) && isSubType0(tp1.normalize, tp2.normalize)) case (_, TypeRef(pre2, sym2, args2)) - if sym2.isAbstractType && !(tp2 =:= tp2.bounds.lo) && (tp1 <:< tp2.bounds.lo) && { - if (!inIDE) true else trackTypeIDE(sym2) - } => true + if (sym2.isAbstractType && !(tp2 =:= tp2.bounds.lo) && (tp1 <:< tp2.bounds.lo) && + (if (!inIDE) true else trackTypeIDE(sym2)) || + sym2 == NotNullClass && tp1.isNotNull) => + true case (_, RefinedType(parents2, ref2)) => (parents2 forall tp1.<:<) && (ref2.toList forall tp1.specializes) && (!parents2.exists(.symbol.isAbstractType) || tp1.symbol != AllRefClass) @@ -2399,24 +2442,20 @@ A type's symbol should never be inspected directly. once patern matching bug is fixed */ case (ThisType(_), _) => tp1.singleDeref <:< tp2 case (SingleType(_, _), _) => tp1.singleDeref <:< tp2 - case (ConstantType(_), _) => tp1.singleDeref <:< tp2 + case (ConstantType(_), _) => + tp1.singleDeref <:< tp2 case (TypeRef(pre1, sym1, args1), _) => if (inIDE) trackTypeIDE(sym1) (sym1 == AllClass && tp2 <:< AnyClass.tpe || sym1 == AllRefClass && tp2.isInstanceOf[SingletonType] && (tp1 <:< tp2.widen)) -/* || - sym1 == AllRefClass && tp2.symbol != AllClass && - tp2 <:< AnyRefClass.tpe)) - if (X) tp2.isNullable - else tp2.symbol != AllClass && tp2 <:< AnyRefClass.tpe))*/ case _ => false } } || { - val tp1n= tp1.normalize - val tp2n= tp2.normalize + val tp1n = tp1.normalize + val tp2n = tp2.normalize ((tp1n ne tp1) || (tp2n ne tp2)) && isSubType0(tp1n, tp2n) } @@ -2626,7 +2665,7 @@ A type's symbol should never be inspected directly. /** The least upper bound wrt <:< of a list of types */ def lub(ts: List[Type], depth: int): Type = { - def lub0(ts0: List[Type]): Type = elimSub(ts0 map (.deconst)) match { + def lub0(ts0: List[Type]): Type = elimSub(ts0 map (_.deconst)) match { case List() => AllClass.tpe case List(t) => t case ts @ PolyType(tparams, _) :: _ => @@ -2702,7 +2741,7 @@ A type's symbol should never be inspected directly. // indent = indent.substring(0, indent.length() - 2) // log(indent + "lub of " + ts + " is " + res)//debug // } - res + if (ts forall (_.isNotNull)) res.notNull else res } def glb(ts: List[Type]): Type = glb(ts, maxClosureDepth(ts) + LubGlbMargin) @@ -2791,7 +2830,7 @@ A type's symbol should never be inspected directly. indent = indent.substring(0, indent.length() - 2) log(indent + "glb of " + ts + " is " + res)//debug } - res + if (ts exists (_.isNotNull)) res.notNull else res } /** The most deeply nested owner that contains all the symbols diff --git a/src/compiler/scala/tools/nsc/transform/Mixin.scala b/src/compiler/scala/tools/nsc/transform/Mixin.scala index b8abc66fa9..d9bd6cc225 100644 --- a/src/compiler/scala/tools/nsc/transform/Mixin.scala +++ b/src/compiler/scala/tools/nsc/transform/Mixin.scala @@ -502,7 +502,7 @@ abstract class Mixin extends InfoTransform { case _ => Select(This(clazz), sym.accessed) } if (sym.isSetter) Assign(accessedRef, Ident(vparams.head)) - else accessedRef + else gen.mkCheckInit(accessedRef) }) } else if (sym.isModule && !(sym hasFlag LIFTED | BRIDGE)) { // add modules diff --git a/src/compiler/scala/tools/nsc/typechecker/Namers.scala b/src/compiler/scala/tools/nsc/typechecker/Namers.scala index a2760218e9..7b0eb3bc2c 100644 --- a/src/compiler/scala/tools/nsc/typechecker/Namers.scala +++ b/src/compiler/scala/tools/nsc/typechecker/Namers.scala @@ -471,7 +471,7 @@ trait Namers requires Analyzer { val tparamSyms = typer.reenterTypeParams(tparams) var vparamSymss = enterValueParams(meth, vparamss) - if (tpt.isEmpty && meth.name == nme.CONSTRUCTOR) tpt.tpe = context.enclClass.owner.tpe + if (tpt.isEmpty && meth.name == nme.CONSTRUCTOR) tpt.tpe = context.enclClass.owner.tpe.notNull if (onlyPresentation) methodArgumentNames(meth) = vparamss.map(.map(.symbol)); diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala index f9f3fd2b67..6ef190be69 100644 --- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala +++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala @@ -987,7 +987,9 @@ trait Typers requires Analyzer { getter.attributes = value.initialize.attributes val result = DefDef(getter, vparamss => if (mods hasFlag DEFERRED) EmptyTree - else typed(atPos(vdef.pos)(Select(This(value.owner), value)), EXPRmode, value.tpe)) + else typed( + atPos(vdef.pos) { gen.mkCheckInit(Select(This(value.owner), value)) }, + EXPRmode, value.tpe)) result.tpt.asInstanceOf[TypeTree] setOriginal tpt /* setPos tpt.pos */ checkNoEscaping.privates(getter, result.tpt) copy.DefDef(result, result.mods withAnnotations mods.annotations, result.name, @@ -1777,8 +1779,9 @@ trait Typers requires Analyzer { val elemtpt1 = typedType(elemtpt) val elems1 = List.mapConserve(elems)(elem => typed(elem, mode, elemtpt1.tpe)) copy.ArrayValue(tree, elemtpt1, elems1) - .setType(if (isFullyDefined(pt) && !phase.erasedTypes) pt - else appliedType(ArrayClass.typeConstructor, List(elemtpt1.tpe))) + .setType( + (if (isFullyDefined(pt) && !phase.erasedTypes) pt + else appliedType(ArrayClass.typeConstructor, List(elemtpt1.tpe))).notNull) } def typedAssign(lhs: Tree, rhs: Tree): Tree = { diff --git a/src/library/scala/runtime/ScalaRunTime.scala b/src/library/scala/runtime/ScalaRunTime.scala index b7984a9bdb..73e9bfa749 100644 --- a/src/library/scala/runtime/ScalaRunTime.scala +++ b/src/library/scala/runtime/ScalaRunTime.scala @@ -32,6 +32,9 @@ object ScalaRunTime { def isValueTag(tag: String) = tag.charAt(0) == '.' def isValueClass(clazz: Class) = clazz.isPrimitive() + def checkInitialized[T <: AnyRef](x: T): T = + if (x == null) throw new UninitializedError else x + abstract class Try[a] { def Catch[b >: a](handler: PartialFunction[Throwable, b]): b def Finally(handler: Unit): a |