#REFACTORING by exept
class: Smalltalk class
changed: #recursiveInstallAutoloadedClassesFrom:rememberIn:maxLevels:noAutoload:packageTop:showSplashInLevels:
Transcript showCR:(... bindWith:...) -> Transcript showCR:... with:...
"{ Encoding: utf8 }"
"
COPYRIGHT (c) 1988 by Claus Gittinger
All Rights Reserved
This software is furnished under a license and may be used
only in accordance with the terms of that license and with the
inclusion of the above copyright notice. This software may not
be provided or otherwise made available to, or used by, any
other person. No title to or ownership of the software is
hereby transferred.
"
"{ Package: 'stx:libbasic' }"
"{ NameSpace: Smalltalk }"
Object subclass:#UndefinedObject
instanceVariableNames:''
classVariableNames:'CreateMinimumProtocolInNewSubclassQuery'
poolDictionaries:''
category:'Kernel-Objects'
!
!UndefinedObject class methodsFor:'documentation'!
copyright
"
COPYRIGHT (c) 1988 by Claus Gittinger
All Rights Reserved
This software is furnished under a license and may be used
only in accordance with the terms of that license and with the
inclusion of the above copyright notice. This software may not
be provided or otherwise made available to, or used by, any
other person. No title to or ownership of the software is
hereby transferred.
"
!
documentation
"
there is only one instance of this class: nil,
representing an undefined or otherwise unspecified object.
All instance variables, array elements and even method/block local
variables are initially set to nil.
Since in Smalltalk/X (and in other smalltalks), nil is represented by
a special pointer value (NULL), there can be only one instance of UndefinedObject,
and no subclassing is possible.
(to be exact: subclassing UndefinedObject is technically possible,
but instances of it would not be recognized as being nil
- therefore, subclassing is blocked and an error is raised when it is tried)
For advanced users:
Beside the above role, nil can be subclassed (!!).
This creates a class which inherits no protocol whatsoever - not even
the basic interfaces as defined by the Object class. Subclasses of nil
are useful if all messages send to instances should trap into the
#doesNotUnderstand: method. For example, proxy objects are typically defined
this way.
[author:]
Claus Gittinger
"
! !
!UndefinedObject class methodsFor:'initialization'!
initialize
CreateMinimumProtocolInNewSubclassQuery isNil ifTrue:[
CreateMinimumProtocolInNewSubclassQuery := QuerySignal new.
CreateMinimumProtocolInNewSubclassQuery nameClass:self message:#createMinimumProtocolInNewSubclassQuery.
CreateMinimumProtocolInNewSubclassQuery defaultAnswer:false.
].
"
UndefinedObject initialize
"
"Created: 3.1.1997 / 15:02:40 / cg"
"Modified: 3.1.1997 / 15:18:33 / cg"
! !
!UndefinedObject class methodsFor:'instance creation'!
basicNew
"catch new - there MUST be only one nil in the system"
^ nil
!
basicNew:size
"catch new - there MUST be only one nil in the system"
^ nil
! !
!UndefinedObject class methodsFor:'Signal constants'!
createMinimumProtocolInNewSubclassQuery
"return the signal used to ask if the minimum required protocol
should be created for nil subclasses.
By default, this is not done, however, the browser answers true
here, to avoid big trouble with nil subclasses which do not define
some methods which the inspector needs."
^ CreateMinimumProtocolInNewSubclassQuery
"Created: 3.1.1997 / 15:05:48 / cg"
"Modified: 3.1.1997 / 15:06:15 / cg"
! !
!UndefinedObject class methodsFor:'queries'!
canBeSubclassed
"return true if it is allowed to create subclasses of the receiver.
Return false here - since it is NOT possible for UndefinedObject.
(due to the representation of nil as a 0-pointer)"
^ false
"Modified: / 5.11.1998 / 16:11:43 / cg"
!
hasImmediateInstances
"return true if this class has immediate instances
i.e. if the instances are represented in the pointer itself and
no real object header/storage is used for the object.
Redefined from Behavior"
^ true
"Created: 3.6.1997 / 12:01:39 / cg"
!
hasSharedInstances
"return true if this class has shared instances, that is, instances
with the same value are identical.
True returned here - there is only one nil."
^ true
!
isBuiltInClass
"return true if this class is known by the run-time-system,
i.e. you cannot add/remove instance variables without recompiling
the VM.
Here, true is returned for myself, false for subclasses."
^ self == UndefinedObject
! !
!UndefinedObject methodsFor:'converting'!
asBoolean
^ false
!
asCollectionOrEmptyIfNil
"answer an empty collection"
^ #()
"Created: / 20-03-2018 / 15:23:56 / stefan"
!
asNilIfEmpty
"I am nil, so answer nil"
^ self
!
doIfNotNil:aBlock
"if I am a collection, then enumerate myself into aBlock.
if I am nil, then do nothing.
Otherwise, evaluate aBlock with myself as argument.
Here, answer nil"
^ nil
"Created: / 20-03-2018 / 15:37:11 / stefan"
"Modified (comment): / 05-08-2018 / 11:26:32 / Claus Gittinger"
!
literalArrayEncoding
"encode myself as an array literal, from which a copy of the receiver
can be reconstructed with #decodeAsLiteralArray."
^ self
"Created: 25.2.1997 / 19:18:47 / cg"
! !
!UndefinedObject methodsFor:'copying'!
copy
"return a shallow copy of myself
- since there is only one nil in the system return self"
^ self
!
deepCopy
"return a deep copy of myself
- since there is only one nil in the system return self"
^ self
!
deepCopyUsing:aDictionary postCopySelector:postCopySelector
"return a deep copy of myself
- since there is only one nil in the system, return self"
^ self
!
shallowCopy
"return a shallow copy of myself
- since there is only one nil in the system return self"
^ self
!
simpleDeepCopy
"return a deep copy of myself
- since there is only one nil in the system return self"
^ self
! !
!UndefinedObject methodsFor:'debugging'!
assertNotNil
"fail and report an error, if the receiver is nil"
<resource: #skipInDebuggersWalkBack>
"/ intentionally left empty
self assert:false message:'value should not be nil here'
"
self assertNotNil
nil assertNotNil
"
"Created: / 18-12-2018 / 15:40:07 / Claus Gittinger"
!
haltIfNil
"halt if the receiver is nil"
<resource: #skipInDebuggersWalkBack>
self halt:'nil encountered'
"
3 haltIfNil
nil haltIfNil
"
"Created: / 17-07-2017 / 10:52:36 / cg"
! !
!UndefinedObject methodsFor:'dependents access'!
addDependent:someObject
"raise an error here - nil may not have dependents (it never changes anyway)"
self proceedableError:'nil may not have dependents'
"Modified: / 28-07-2010 / 19:20:36 / cg"
"Modified: / 24-05-2018 / 21:05:28 / Claus Gittinger"
!
dependents
"nil has no dependents"
^ #()
"Modified (format): / 30-11-2018 / 18:03:27 / Stefan Vogel"
!
onChangeSend:selector to:someOne
"raise an error here - nil may not have dependents (it never changes anyway)"
self proceedableError:'nil may not have dependents'
"Created: / 30-11-2018 / 18:03:49 / Stefan Vogel"
!
release
"ignored here - nil has no dependents"
!
removeDependent:someObject
"ignored here - nil has no dependents"
! !
!UndefinedObject methodsFor:'error catching'!
basicAt:index
"catch array access - it's illegal.
Redefined here since basicAt: in Object omits the nil-check"
^ self notIndexed
"Modified (comment): / 17-05-2017 / 16:36:12 / mawalch"
!
basicAt:index put:anObject
"catch array access - it's illegal.
Redefined here since basicAt:put: in Object omits the nil-check"
^ self notIndexed
"Modified (comment): / 17-05-2017 / 16:36:17 / mawalch"
! !
!UndefinedObject methodsFor:'printing & storing'!
printOn:aStream
"append a printed representation of the receiver to the
argument, aStream"
aStream nextPutAll:'nil'
!
printString
"return a string for printing myself"
^ 'nil'
!
storeOn:aStream
"append a printed representation of the receiver to the
argument, aStream, which allows reconstruction of it"
^ self printOn:aStream
!
storeString
"return a string for storing myself"
^ 'nil'
! !
!UndefinedObject methodsFor:'queries'!
basicSize
"return the number of indexed instvars
defined here since size in Object omits the nil-check"
^ 0
"Modified (comment): / 17-05-2017 / 16:37:13 / mawalch"
!
size
"return the number of indexed instvars
defined here since size in Object omits the nil-check"
^ 0
"Modified (comment): / 17-05-2017 / 16:37:19 / mawalch"
! !
!UndefinedObject methodsFor:'subclass creation'!
nilSubclass:action
"common helper for subclass creation.
Creates a nil-superclass class.
If the CreateMinimumProtocolInNewSubclassQuery answers true,
entries for the minimum required protocol (#class, #isBehavior
and #doesNotUnderstand:) are also automatically created.
(this query is typically answered by the browser)
These are required to avoid getting into deep trouble when
inspecting or debugging instances of this new class.
The methods get a modified source code to remind you that these
methods were automatically generated."
|newClass methodDict method|
Class withoutUpdatingChangesDo:[
newClass := action value
].
newClass notNil ifTrue:[
newClass setSuperclass:nil.
newClass class setSuperclass:Class.
newClass hasMethods ifFalse:[
Class addChangeRecordForClass:newClass.
CreateMinimumProtocolInNewSubclassQuery query
ifTrue:[
"
copy over method objects from Object
and modify the source code
"
methodDict := MethodDictionary new:3.
#(#class #isBehavior #doesNotUnderstand:) do:[:sel|
method := (Object compiledMethodAt:sel) copy.
method source: method source , '
"
*** WARNING
***
*** this method has been automatically created,
*** since all nil-subclasses should respond to some minimum required
*** protocol.
***
*** Inspection and/or debugging of instances may not be possible,
*** if you remove/change this method.
"
'.
methodDict at:sel put:method.
"/ newClass addChangeRecordForMethod:method
].
newClass methodDictionary:methodDict.
]
]
].
^ newClass
"Modified: / 3.1.1997 / 15:53:21 / cg"
"Created: / 3.1.1997 / 16:00:34 / cg"
"Modified: / 18.3.1999 / 18:29:58 / stefan"
!
subclass:nameSymbol
"create a new class as a subclass of an existing class (the receiver).
The subclass will have indexed variables if the receiving-class has."
^ self
subclass:nameSymbol
instanceVariableNames:''
classVariableNames:''
poolDictionaries:''
category:'* as yet unspecified *'
"Created: / 09-02-2019 / 15:05:15 / Claus Gittinger"
!
subclass:nameSymbol instanceVariableNames:instVarNameString
"create a new class as a subclass of an existing class (the receiver).
The subclass will have indexed variables if the receiving-class has."
^ self
subclass:nameSymbol
instanceVariableNames:instVarNameString
classVariableNames:''
poolDictionaries:''
category:'* as yet unspecified *'
"Created: / 09-02-2019 / 15:05:36 / Claus Gittinger"
!
subclass:nameSymbol instanceVariableNames:instVarNameString classVariableNames:classVarString poolDictionaries:pool
"create a new class which has nil as superclass
- i.e. traps into #doesNotUnderstand: for all of its messages."
"this method allows fileIn of ST/V and V'Age classes
(which seem to have no category)"
^ self
subclass:nameSymbol
instanceVariableNames:instVarNameString
classVariableNames:classVarString
poolDictionaries:pool
category:(Class defaultCategoryForSTVorVAGEClasses).
!
subclass:nameSymbol instanceVariableNames:instVarNameString classVariableNames:classVarString poolDictionaries:pool category:cat
"create a new class which has nil as superclass
- i.e. traps into #doesNotUnderstand: for all of its messages."
^ self
nilSubclass:[
Object class
name:nameSymbol
inEnvironment:(Class nameSpaceQuerySignal query)
subclassOf:self
instanceVariableNames:instVarNameString
variable:false
words:true
pointers:true
classVariableNames:classVarString
poolDictionaries:pool
category:cat
comment:nil
changed:true
]
"Modified: / 3.1.1997 / 16:00:39 / cg"
"Modified: / 18.3.1999 / 18:30:07 / stefan"
!
variableByteSubclass:nameSymbol instanceVariableNames:instVarNameString classVariableNames:classVarString poolDictionaries:pool category:cat
"create a new class which has nil as superclass
- i.e. traps into #doesNotUnderstand: for all of its messages."
^ self
nilSubclass:[
Object class
name:nameSymbol
inEnvironment:(Class nameSpaceQuerySignal query)
subclassOf:self
instanceVariableNames:instVarNameString
variable:true
words:false
pointers:false
classVariableNames:classVarString
poolDictionaries:pool
category:cat
comment:nil
changed:true
]
"Modified: / 3.1.1997 / 16:00:42 / cg"
"Modified: / 18.3.1999 / 18:30:11 / stefan"
!
variableSubclass:nameSymbol instanceVariableNames:instVarNameString classVariableNames:classVarString poolDictionaries:pool category:cat
"create a new class which has nil as superclass
- i.e. traps into #doesNotUnderstand: for all of its messages."
^ self
nilSubclass:[
Object class
name:nameSymbol
inEnvironment:(Class nameSpaceQuerySignal query)
subclassOf:self
instanceVariableNames:instVarNameString
variable:true
words:false
pointers:true
classVariableNames:classVarString
poolDictionaries:pool
category:cat
comment:nil
changed:true
]
"Modified: / 3.1.1997 / 16:00:45 / cg"
"Modified: / 18.3.1999 / 18:30:16 / stefan"
! !
!UndefinedObject methodsFor:'subclass creation-private'!
subclass:nameSymbol instanceVariableNames:instVarNameString classVariableNames:classVarString poolDictionaries:pool privateIn:ownerClassArg
"create a new private class which has nil as superclass
- i.e. traps into #doesNotUnderstand: for all of its messages."
|category ownerClass|
(ownerClass := ownerClassArg) isNil ifTrue:[
self proceedableError:'Nil (undefined) owner class - proceed to define as global'.
] ifFalse:[
category := ownerClassArg category
].
^ self
nilSubclass:[
Object class
name:nameSymbol
inEnvironment:ownerClass
subclassOf:self
instanceVariableNames:instVarNameString
variable:false
words:true
pointers:true
classVariableNames:classVarString
poolDictionaries:pool
category:category
comment:nil
changed:true
]
"Modified: / 03-01-1997 / 16:00:39 / cg"
"Modified: / 18-03-1999 / 18:30:07 / stefan"
"Modified: / 24-05-2018 / 21:05:47 / Claus Gittinger"
! !
!UndefinedObject methodsFor:'testing'!
? defaultValue
"a syntactic sugar-piece:
if the receiver is nil, return the defaultValue;
otherwise, return the receiver.
This method is redefined from Object;
the argument is returned unconditionally here.
Thus, if foo and bar are simple variables or constants,
foo ? bar
is the same as:
(foo isNil ifTrue:[bar] ifFalse:[foo])
if they are message sends, the equivalent code is:
[
|t1 t2|
t1 := foo.
t2 := bar.
t1 isNil ifTrue:[t2] ifFalse:[t1]
] value
Can be used to provide defaultValues to variables,
as in:
foo := arg ? #defaultValue
"
^ defaultValue
"
1 ? #default
nil ? #default
"
"Created: / 4.11.1996 / 20:37:09 / cg"
"Modified: / 19.5.1998 / 17:39:36 / cg"
!
?+ aOneArgBlock
"a syntactic sugar-piece:
aOneArgBlock is executed with self as argument
if self is not nil.
Note: this method should never be redefined in classes other than UndefinedObject.
"
^ self
!
?? defaultValue
"a syntactic sugar-piece:
much like ?, but sends value to the argument if required.
If the receiver is nil, return the defaultValues value;
otherwise, return the receiver.
This method is redefined from Object.
Thus, if foo and bar are simple variables or constants,
foo ?? bar
is the same as:
(foo isNil ifTrue:[bar value] ifFalse:[foo])
if they are message sends, the equivalent code is:
[
|t|
t := foo.
t isNil ifTrue:[bar value] ifFalse:[t]
] value
Can be used to provide defaultValues to variables,
as in:
foo := arg ?? [something]
"
^ defaultValue value
"
1 ?? #default
nil ?? #default
1 ?? [Date today]
nil ?? [Date today]
"
"Created: / 4.11.1996 / 20:37:09 / cg"
"Modified: / 19.5.1998 / 17:42:10 / cg"
!
checkNilFileStream
"Do nothing if this is a valid FileStream
(i.e. the previous open operation was successful).
Also implemented in UndefinedObject, to raise an Error there.
This is an aid for converting from the old error reporting (returning nil)
to the new error reporting (with real Exceptions).
It will vanish as soon as the conversion has been done"
^ OpenError raise
!
hash
"return an integer useful as a hash key"
^ 0
!
identityHash
"return an integer useful as a hash key"
^ 0
!
ifNil:aBlockOrValue
"return myself, or the result from evaluating the argument, if I am nil.
This is much like #?, but sends #value to the argument in case of a nil
receiver.
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected."
^ aBlockOrValue value
!
ifNil:nilBlockOrValue ifNotNil:notNilBlockOrValue
"return the value of the first arg, if I am nil,
the result from evaluating the 2nd argument, if I am not nil.
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected."
^ nilBlockOrValue value
!
ifNotNil:aBlockOrValue
"return myself if nil, or the result from evaluating the argument, if I am not nil.
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected."
^ nil
!
ifNotNil:notNilBlockOrValue ifNil:nilBlockOrValue
"return the value of the 2nd arg, if I am nil,
the result from evaluating the 1st argument, if I am not nil.
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected."
^ nilBlockOrValue value
!
ifNotNilDo:aBlock
"if the receiver is non-nil, return the value of aBlock, passing myself as argument.
Otherwise do nothing and return nil."
^ nil
!
isEmptyOrNil
"return true if I am nil or an empty collection
- since I am nil, return true. (from Squeak)"
^ true
"Created: / 13-11-2001 / 13:16:40 / cg"
"Modified (comment): / 17-08-2011 / 09:29:30 / cg"
"Modified (comment): / 15-06-2017 / 01:46:00 / mawalch"
!
isImmediate
"return true if I am an immediate object
i.e. I am represented in the pointer itself and
no real object header/storage is used by me."
^ true
"Created: / 18-09-2018 / 14:48:45 / Stefan Vogel"
"Modified (comment): / 27-05-2019 / 15:38:24 / Claus Gittinger"
!
isLiteral
"return true if the receiver can be used as a literal constant in ST syntax
(i.e. can be used in constant arrays)"
^ true
!
isNil
"Return true if the receiver is nil.
Since I am definitely nil, unconditionally return true here.
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected."
^ true
!
notEmptyOrNil
"Squeak compatibility:
return true if I am neither nil nor an empty collection."
^ false
!
notNil
"Return true if the receiver is not nil.
Since I am definitely nil, unconditionally return false here.
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected."
^ false
! !
!UndefinedObject methodsFor:'tracing'!
traceInto:aRequestor level:level from:referrer
"double dispatch into tracer, passing my type implicitely in the selector"
^ aRequestor traceUndefinedObject:self level:level from:referrer
! !
!UndefinedObject methodsFor:'visiting'!
acceptVisitor:aVisitor with:aParameter
"dispatch for visitor pattern; send #visitNil:with: to aVisitor."
^ aVisitor visitNilWith:aParameter
! !
!UndefinedObject class methodsFor:'documentation'!
version
^ '$Header$'
!
version_CVS
^ '$Header$'
! !
UndefinedObject initialize!