Class: ImmutableArray

• Inheritance
• Description
• Related information
• Instance protocol
  • accessing
  • converting
  • copying
  • error handling
  • private
  • queries
  • specials

Inheritance:

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

Package:

stx:libbasic

Category:

System-Compiler-Support

Version:

rev: 1.28 date: 2009/11/16 08:59:40

user: stefan

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.


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.
    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
    Parser
    Scanner

Instance protocol:

 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.

 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.

 asImmutableArray

 copyEmpty

when copying, return a real (mutable) Array

 copyEmptyAndGrow: size

when copying, return a real (mutable) Array

 postCopy

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

 postDeepCopy

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

 shallowCopy

when copying, return a real (mutable) Array

 creator

find the method that contains me

 noModificationError

a store is attempted - for our convenience, find the method that
contains me, for a nicer error message

 species

Copies should be mutable

 isLiteral

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

 become: anotherObject

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

 becomeNil

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