eXept Software AG Logo

Smalltalk/X Webserver

Documentation of class 'ImmutableArray':

Home

Documentation
www.exept.de
Everywhere
for:
[back]

Class: ImmutableArray


Inheritance:

   Object
   |
   +--Collection
      |
      +--SequenceableCollection
         |
         +--ArrayedCollection
            |
            +--Array
               |
               +--ImmutableArray

Package:
stx:libbasic
Category:
System-Compiler-Support
Version:
rev: 1.44 date: 2017/06/12 11:44:18
user: mawalch
file: ImmutableArray.st directory: libbasic
module: stx stc-classLibrary: libbasic
Author:
Claus Gittinger

Description:


By default, array literals in smalltalk are mutable objects. That
may lead to some subtle (and hard to find errors), if some method passes
a literal array constant as argument to someone else, who changes the
array using at:put: like messages. Since the array object is kept in
the first methods literals, the array 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 ImmutableArray instead of Arrays
for array literals. Instances of ImmutableArray 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 array literals entered in
 a workspace somewhat strange: you cannot modify it any longer).

Turn the ImmutableArray feature on by setting the Parsers class variable
'ArraysAreImmutable' to true or use the new launchers settings menu.

This class should be used only by the compiler.

ATTENTION:
    there may be still code around which checks for explicit class being Array
    (both in Smalltalk and in primitive code). All code like foo 'class == Array'
    or '__isArray' will not work with ImmutableArrays; consider using '__isArrayLike'.
    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...


Related information:

    ImmutableString
    ImmutableByteArray
    Parser
    Scanner

Class protocol:

queries
o  mutableClass
answer an equivalent mustable class

testing
o  hasImmutableInstances


Instance protocol:

accessing
o  at: index put: value
Trigger an error if an immutable array is stored into.
The store will be performed (for compatibility reasons) if you continue
in the debugger.

o  basicAt: index put: value
Trigger an error if an immutable array is stored into.
The store will be performed (for compatibility reasons) if you continue
in the debugger.

converting
o  asArray
return the receiver as an array. I am already.
Use asNewArray, or asMutableCollection if you need a copy for modification

o  asImmutableArray

o  asMutableCollection
return a writable copy of myself

o  asNewArray
return the receiver as a unique new array.

o  beImmutable
that's what I am

o  beMutable
you never go back

copying
o  postCopy
when copied, make it me a real (mutable) Array

o  postDeepCopy
when copied, make it me a real (mutable) Array

o  shallowCopy
when copying, return a real (mutable) Array
usage example(s):
     #(1 2 3 4) asImmutableArray shallowCopy

inspecting
o  inspectorValueStringInListFor: anInspector
( an extension from the stx:libtool package )
returns a string to be shown in the inspector's list

private
o  species
Copies should be mutable

o  speciesForCopy
Copies should be mutable

queries
o  isImmutable

o  isLiteral
return true, if the receiver can be used as a literal constant in ST syntax
(i.e. can be used in constant arrays)

specials
o  become: anotherObject
trigger an error if I should become something else
(this would be an even more tricky manipulation)

o  becomeNil
trigger an error if I should become nil
(this would be an even more tricky manipulation)

o  becomeSameAs: anotherObject
trigger an error if I should become something else
(this would be an even more tricky manipulation)

o  grow: newSize
trigger an error if I should change my size



ST/X 7.1.0.0; WebServer 1.663 at exept.de:8081; Sun, 23 Sep 2018 10:45:24 GMT