"======================================================================
|
|   UndefinedObject (nil) Method Definitions
|
|
 ======================================================================"

"======================================================================
|
| Copyright 1988,92,94,95,99,2000,2001,2002,2003,2006,2008
| Free Software Foundation, Inc.
| Written by Steve Byrne.
|
| This file is part of the GNU Smalltalk class library.
|
| The GNU Smalltalk class library is free software; you can redistribute it
| and/or modify it under the terms of the GNU Lesser General Public License
| as published by the Free Software Foundation; either version 2.1, or (at
| your option) any later version.
| 
| The GNU Smalltalk class library is distributed in the hope that it will be
| useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
| General Public License for more details.
| 
| You should have received a copy of the GNU Lesser General Public License
| along with the GNU Smalltalk class library; see the file COPYING.LIB.
| If not, write to the Free Software Foundation, 59 Temple Place - Suite
| 330, Boston, MA 02110-1301, USA.  
|
 ======================================================================"



Object subclass: UndefinedObject [
    
    <category: 'Language-Implementation'>
    <comment: 'I have the questionable distinction of being a class with only one
instance, which is the object "nil".'>

    copy [
	<category: 'basic'>
	^self
    ]

    shallowCopy [
	<category: 'basic'>
	^self
    ]

    deepCopy [
	<category: 'basic'>
	^self
    ]

    isNull [
	"Answer whether the receiver represents a NULL C pointer. Always
	 answer true."

	<category: 'testing'>
	^true
    ]

    isNil [
	"Answer whether the receiver is the undefined object nil. Always
	 answer true."

	<category: 'testing'>
	^true
    ]

    notNil [
	"Answer whether the receiver is not the undefined object nil. Always
	 answer false."

	<category: 'testing'>
	^false
    ]

    ifNil: nilBlock [
	"Evaluate nilBlock if the receiver is nil, else answer nil"

	<category: 'testing'>
	^nilBlock value
    ]

    ifNil: nilBlock ifNotNil: notNilBlock [
	"Evaluate nilBlock if the receiver is nil, else evaluate
	 notNilBlock, passing the receiver."

	<category: 'testing'>
	^nilBlock value
    ]

    ifNotNil: notNilBlock [
	"Evaluate notNilBlock if the receiver is not nil, passing the receiver.
	 Else answer nil"

	<category: 'testing'>
	^nil
    ]

    ifNotNil: notNilBlock ifNil: nilBlock [
	"Evaluate nilBlock if the receiver is nil, else evaluate
	 notNilBlock, passing the receiver."

	<category: 'testing'>
	^nilBlock value
    ]

    ifNil: nilBlock ifNotNilDo: iterableBlock [
	"Evaluate nilBlock if the receiver is nil, else evaluate
	 iterableBlock with each element of the receiver (which
         should be an Iterable)."

	<category: 'iteration'>
	^nilBlock value
    ]

    ifNotNilDo: iterableBlock [
	"Evaluate iterableBlock with each element of the receiver (which
         should be an Iterable) if not nil.  Else answer nil"

	<category: 'iteration'>
	^nil
    ]

    ifNotNilDo: iterableBlock ifNil: nilBlock [
	"Evaluate nilBlock if the receiver is nil, else evaluate
	 iterableBlock, passing each element of the receiver (which
         should be an Iterable)."

	<category: 'iteration'>
	^nilBlock value
    ]

    addDependent: ignored [
	"Fail, nil does not support dependents."

	<category: 'dependents access'>
	self shouldNotImplement
    ]

    release [
	"Ignore this call, nil does not support dependents."

	<category: 'dependents access'>
	
    ]

    printOn: aStream in: aNamespace [
	"Print on aStream a representation of the receiver as it would be accessed
	 from aNamespace: nil is the same everywhere, so print the same as
	 #printOn:"

	<category: 'printing'>
	aStream nextPutAll: 'nil'
    ]

    printOn: aStream [
	"Print a representation of the receiver on aStream."

	<category: 'printing'>
	aStream nextPutAll: 'nil'
    ]

    isLiteralObject [
	"Answer whether the receiver is expressible as a Smalltalk literal."

	<category: 'storing'>
	^true
    ]

    storeLiteralOn: aStream [
	"Store on aStream some Smalltalk code which compiles to the receiver"

	<category: 'storing'>
	self storeOn: aStream
    ]

    storeOn: aStream [
	"Store Smalltalk code compiling to the receiver on aStream."

	<category: 'storing'>
	self printOn: aStream
    ]

    subclass: classNameString instanceVariableNames: stringInstVarNames classVariableNames: stringOfClassVarNames poolDictionaries: stringOfPoolNames [
	"Don't use this, it is only present to file in from IBM Smalltalk"

	<category: 'class creation - alternative'>
	^self 
	    subclass: classNameString
	    instanceVariableNames: stringInstVarNames
	    classVariableNames: stringOfClassVarNames
	    poolDictionaries: stringOfPoolNames
	    category: 'no category'
    ]

    subclass: classNameString classInstanceVariableNames: stringClassInstVarNames instanceVariableNames: stringInstVarNames classVariableNames: stringOfClassVarNames poolDictionaries: stringOfPoolNames [
	"Don't use this, it is only present to file in from IBM Smalltalk"

	<category: 'class creation - alternative'>
	^(self 
	    subclass: classNameString
	    instanceVariableNames: stringInstVarNames
	    classVariableNames: stringOfClassVarNames
	    poolDictionaries: stringOfPoolNames
	    category: 'no category')
	    classInstanceVariableNames: stringClassInstVarNames;
	    yourself
    ]

    variableSubclass: classNameString instanceVariableNames: stringInstVarNames classVariableNames: stringOfClassVarNames poolDictionaries: stringOfPoolNames [
	"Don't use this, it is only present to file in from IBM Smalltalk"

	<category: 'class creation - alternative'>
	^self 
	    variableSubclass: classNameString
	    instanceVariableNames: stringInstVarNames
	    classVariableNames: stringOfClassVarNames
	    poolDictionaries: stringOfPoolNames
	    category: 'no category'
    ]

    variableSubclass: classNameString classInstanceVariableNames: stringClassInstVarNames instanceVariableNames: stringInstVarNames classVariableNames: stringOfClassVarNames poolDictionaries: stringOfPoolNames [
	"Don't use this, it is only present to file in from IBM Smalltalk"

	<category: 'class creation - alternative'>
	^(self 
	    variableSubclass: classNameString
	    instanceVariableNames: stringInstVarNames
	    classVariableNames: stringOfClassVarNames
	    poolDictionaries: stringOfPoolNames
	    category: 'no category')
	    classInstanceVariableNames: stringClassInstVarNames;
	    yourself
    ]

    variableByteSubclass: classNameString instanceVariableNames: stringInstVarNames classVariableNames: stringOfClassVarNames poolDictionaries: stringOfPoolNames [
	"Don't use this, it is only present to file in from IBM Smalltalk"

	<category: 'class creation - alternative'>
	^self 
	    variableByteSubclass: classNameString
	    instanceVariableNames: stringInstVarNames
	    classVariableNames: stringOfClassVarNames
	    poolDictionaries: stringOfPoolNames
	    category: 'no category'
    ]

    variableByteSubclass: classNameString classInstanceVariableNames: stringClassInstVarNames instanceVariableNames: stringInstVarNames classVariableNames: stringOfClassVarNames poolDictionaries: stringOfPoolNames [
	"Don't use this, it is only present to file in from IBM Smalltalk"

	<category: 'class creation - alternative'>
	^(self 
	    variableByteSubclass: classNameString
	    instanceVariableNames: stringInstVarNames
	    classVariableNames: stringOfClassVarNames
	    poolDictionaries: stringOfPoolNames
	    category: 'no category')
	    classInstanceVariableNames: stringClassInstVarNames;
	    yourself
    ]

    variableLongSubclass: classNameString instanceVariableNames: stringInstVarNames classVariableNames: stringOfClassVarNames poolDictionaries: stringOfPoolNames [
	"Don't use this, it is only present to file in from IBM Smalltalk"

	<category: 'class creation - alternative'>
	^self 
	    variable: #uint
	    subclass: classNameString
	    instanceVariableNames: stringInstVarNames
	    classVariableNames: stringOfClassVarNames
	    poolDictionaries: stringOfPoolNames
	    category: 'no category'
    ]

    variableLongSubclass: classNameString classInstanceVariableNames: stringClassInstVarNames instanceVariableNames: stringInstVarNames classVariableNames: stringOfClassVarNames poolDictionaries: stringOfPoolNames [
	"Don't use this, it is only present to file in from IBM Smalltalk"

	<category: 'class creation - alternative'>
	^(self 
	    variable: #uint
	    subclass: classNameString
	    instanceVariableNames: stringInstVarNames
	    classVariableNames: stringOfClassVarNames
	    poolDictionaries: stringOfPoolNames
	    category: 'no category')
	    classInstanceVariableNames: stringClassInstVarNames;
	    yourself
    ]

    instSize [
	<category: 'class polymorphism'>
	^0
    ]

    methodDictionary [
	<category: 'class polymorphism'>
	^nil
    ]

    removeSubclass: aClass [
	"Ignored -- necessary to support disjoint class hierarchies"

	<category: 'class polymorphism'>
	
    ]

    subclass: classNameString instanceVariableNames: stringInstVarNames classVariableNames: stringOfClassVarNames poolDictionaries: stringOfPoolNames category: categoryNameString [
	"Define a fixed subclass of the receiver with the given name, instance
	 variables, class variables, pool dictionaries and category. If the
	 class is already defined, if necessary, recompile everything needed."

	<category: 'class polymorphism'>
	| meta |
	KernelInitialized 
	    ifFalse: [^(Smalltalk at: classNameString) category: categoryNameString].
	meta := self metaclassFor: classNameString.
	^meta 
	    name: classNameString
	    environment: Namespace current
	    subclassOf: self
	    instanceVariableNames: stringInstVarNames
	    shape: nil
	    classVariableNames: stringOfClassVarNames
	    poolDictionaries: stringOfPoolNames
	    category: categoryNameString
    ]

    variable: shape subclass: classNameString instanceVariableNames: stringInstVarNames classVariableNames: stringOfClassVarNames poolDictionaries: stringOfPoolNames category: categoryNameString [
	"Define a variable subclass of the receiver with the given name,
	 shape, instance variables, class variables, pool dictionaries and
	 category. If the class is already defined, if necessary, recompile
	 everything needed.  The shape can be one of #byte #int8 #character
	 #short #ushort #int #uint #int64 #uint64 #utf32 #float #double or
	 #pointer."

	<category: 'class polymorphism'>
	| meta |
	KernelInitialized 
	    ifFalse: [^(Smalltalk at: classNameString) category: categoryNameString].
	meta := self metaclassFor: classNameString.
	^meta 
	    name: classNameString
	    environment: Namespace current
	    subclassOf: self
	    instanceVariableNames: stringInstVarNames
	    shape: shape
	    classVariableNames: stringOfClassVarNames
	    poolDictionaries: stringOfPoolNames
	    category: categoryNameString
    ]

    subclass: classNameString [
	"Define a subclass of the receiver with the given name.  If the class
	 is already defined, don't modify its instance or class variables
	 but still, if necessary, recompile everything needed."

	<category: 'class polymorphism'>
	| meta |
	KernelInitialized ifFalse: [^Smalltalk at: classNameString].
	meta := self metaclassFor: classNameString.
	^meta 
	    name: classNameString
	    environment: Namespace current
	    subclassOf: self
    ]

    variableSubclass: classNameString instanceVariableNames: stringInstVarNames classVariableNames: stringOfClassVarNames poolDictionaries: stringOfPoolNames category: categoryNameString [
	"Define a variable pointer subclass of the receiver with the given
	 name, instance variables, class variables, pool dictionaries and
	 category. If the class is already defined, if necessary, recompile
	 everything needed."

	<category: 'class polymorphism'>
	| meta |
	KernelInitialized 
	    ifFalse: [^(Smalltalk at: classNameString) category: categoryNameString].
	meta := self metaclassFor: classNameString.
	^meta 
	    name: classNameString
	    environment: Namespace current
	    subclassOf: self
	    instanceVariableNames: stringInstVarNames
	    shape: #pointer
	    classVariableNames: stringOfClassVarNames
	    poolDictionaries: stringOfPoolNames
	    category: categoryNameString
    ]

    variableWordSubclass: classNameString instanceVariableNames: stringInstVarNames classVariableNames: stringOfClassVarNames poolDictionaries: stringOfPoolNames category: categoryNameString [
	"Define a word variable subclass of the receiver with the given
	 name, instance variables, class variables, pool dictionaries and
	 category. If the class is already defined, if necessary, recompile
	 everything needed."

	<category: 'class polymorphism'>
	| meta |
	KernelInitialized 
	    ifFalse: [^(Smalltalk at: classNameString) category: categoryNameString].
	meta := self metaclassFor: classNameString.
	^meta 
	    name: classNameString
	    environment: Namespace current
	    subclassOf: self
	    instanceVariableNames: stringInstVarNames
	    shape: #word
	    classVariableNames: stringOfClassVarNames
	    poolDictionaries: stringOfPoolNames
	    category: categoryNameString
    ]

    variableByteSubclass: classNameString instanceVariableNames: stringInstVarNames classVariableNames: stringOfClassVarNames poolDictionaries: stringOfPoolNames category: categoryNameString [
	"Define a byte variable subclass of the receiver with the given
	 name, instance variables, class variables, pool dictionaries
	 and category. If the class is already defined, if necessary,
	 recompile everything needed."

	<category: 'class polymorphism'>
	| meta |
	KernelInitialized 
	    ifFalse: [^(Smalltalk at: classNameString) category: categoryNameString].
	meta := self metaclassFor: classNameString.
	^meta 
	    name: classNameString
	    environment: Namespace current
	    subclassOf: self
	    instanceVariableNames: stringInstVarNames
	    shape: #byte
	    classVariableNames: stringOfClassVarNames
	    poolDictionaries: stringOfPoolNames
	    category: categoryNameString
    ]

    metaclassFor: classNameString [
	"Create a Metaclass object for the given class name. The metaclass
	 is a subclass of Class"

	<category: 'class polymorphism'>
	| className class |
	className := classNameString asSymbol.
	class := Namespace current hereAt: className ifAbsent: [nil].
	^(class isNil or: [class isClass not]) 
	    ifTrue: [Metaclass subclassOf: Class]
	    ifFalse: [class class]
    ]

    allSubclasses [
	"Return all the classes in the system."

	<category: 'class polymorphism'>
	^Class allSubclasses collect: [:each | each instanceClass]
    ]

    mutate: instVarMap startAt: start newClass: class [
	"Private - Do nothing, this is here in case the WeakArray garbage
	 collects an object that is to be mutated."

	<category: 'private'>
	
    ]

    inheritsFrom: aClass [
        "Always return false, as nil inherits from nothing."

        ^false
    ]
]