"

 COPYRIGHT (c) 1998 by eXept Software AG

	      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' }"

String variableByteSubclass:#ImmutableString

	instanceVariableNames:''

	classVariableNames:''

	poolDictionaries:''

	category:'System-Compiler-Support'

!

!ImmutableString class methodsFor:'documentation'!

copyright

"

 COPYRIGHT (c) 1998 by eXept Software AG

	      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

"

    By default, string literals in smalltalk are mutable objects. That

    may lead to some subtle (and hard to find errors), if some method passes

    a string constant as argument to someone else, who changes the

    string using at:put: like messages. Since the string object is kept in

    the first methods literals, the string constant has now been changed without

    having the method's sourcecode reflect this. Thus, the method will

    behave differently from what its source may make you think.

    To help finding this kind of 'feature/bug', the compiler can be

    configured to create instances of this ImmutableString instead of Strings

    for literals. Instances of ImmutableString catch storing accesses and

    enter the debugger. Although useful, this feature is disabled by default

    for compatibility to other smalltalk implementations.

    (Also, if turned on, this makes inspecting string literals entered in

     a workspace somewhat strange: you cannot modify it any longer).

    Turn the ImmutableString feature on by setting the Parsers class variable

    'StringsAreImmutable' to true or use the new launchers settings menu.

    ATTENTION:

	there may be still code around which checks for explicit class being String

	(both in Smalltalk and in primitive code). All code like foo 'class == String'

	or '__isString' will not work with ImmutableStrings.

	A somewhat better approach would be to either add a flag to the object (mutability)

	and check this dynamically (expensive) or to place immutable objects into a readonly

	memory segment (the good solution). We will eventually implement the second in the future...

    [see also:]

	ImmutableArray

	Parser Scanner

    [author:]

	Claus Gittinger

"

! !

!ImmutableString methodsFor:'accessing'!

at:index put:value

    "Trigger an error if an immutable string is stored into.

     The store will be performed (for compatibility reasons) if you continue

     in the debugger."

    self noModificationError.

    ^ super at:index put:value

    "Created: / 3.8.1998 / 14:45:14 / cg"

!

basicAt:index put:value

    "Trigger an error if an immutable string is stored into.

     The store will be performed (for compatibility reasons) if you continue

     in the debugger."

    self noModificationError.

    ^ super basicAt:index put:value

! !

!ImmutableString methodsFor:'converting'!

asImmutableString

    ^ self

! !

!ImmutableString methodsFor:'copying'!

copyEmpty

    "when copying, return a real (mutable) String"

    ^ String new:self size

    "Created: / 3.8.1998 / 14:46:22 / cg"

!

copyEmptyAndGrow:size

    "when copying, return a real (mutable) String"

    ^ String new:size

    "Created: / 3.8.1998 / 14:46:34 / cg"

!

postCopy

    "when copied, make me a real (mutable) String"

    self changeClassTo:String.

    "Created: / 3.8.1998 / 14:46:45 / cg"

!

postDeepCopy

    "when copied, make it me a real (mutable) String"

    self changeClassTo:String.

    "

     'foobar' asImmutableString copy          class

     'foobar' asImmutableString shallowCopy   class

     'foobar' asImmutableString deepCopy      class

    "

!

shallowCopy

    "when copying, return a real (mutable) String"

    |sz|

    sz := self size.

    ^ (String new:sz) replaceFrom:1 to:sz with:self startingAt:1

    "Created: / 3.8.1998 / 14:47:00 / cg"

! !

!ImmutableString methodsFor:'error handling'!

creator

    "find the method that contains me.

     This works only, if the string is included in a method's literal array.

     Stc compiled code does not put strings into the literal array - Bytecode compiled code does."

    ^ Method allSubInstances detect:[:aMethod | (aMethod referencesGlobal:self)] ifNone:nil.

    "

      'hello' creator

    "

    "Created: / 3.8.1998 / 14:47:19 / cg"

!

noModificationError

    "a store is attempted - for our convenience, find the method that

     contains me, for a nicer error message"

    |creator msg context|

    creator := self creator.

    creator notNil ifTrue:[

	msg := ' (' , creator whoString , ')'

    ].

    context := thisContext sender.

     "

     this error is reported on an attempt to store into a literal

     string. The literal was created in creator.

     If you press continue in the debugger, the store will be performed.

     If you don't want this, press abort and check your code.

     Storing into literals is VERY VERY bad coding style.

    "

    NoModificationError

	raiseRequestWith:self

	errorString:msg

	in:context.

    "Created: / 3.8.1998 / 14:47:45 / cg"

! !

!ImmutableString methodsFor:'private'!

species

    "Copies should be mutable"

    ^ String

    "Created: / 3.8.1998 / 14:47:58 / cg"

! !

!ImmutableString methodsFor:'specials'!

become:anotherObject

    "trigger an error if I should become something else

     (this would be an even more tricky manipulation)"

    self noModificationError.

    ^ super become:anotherObject

    "Created: / 3.8.1998 / 14:48:29 / cg"

!

becomeNil

    "trigger an error if I should become nil

     (this would be an even more tricky manipulation)"

    self noModificationError.

    ^ super becomeNil

    "Created: / 3.8.1998 / 14:48:37 / cg"

! !

!ImmutableString class methodsFor:'documentation'!

version

!

version_CVS