Class: Iterator

• Inheritance
• Description
• Class protocol
  • instance creation
• Instance protocol
  • accessing
  • adding & removing
  • converting
  • enumerating
  • inspecting
  • printing & storing
  • private
  • queries
• Examples

Inheritance:

   Object
   |
   +--Collection
      |
      +--Iterator

Package:

stx:libbasic2

Category:

Collections-Sequenceable

Version:

rev: 1.36 date: 2019/01/09 16:39:50

user: cg

file: Iterator.st directory: libbasic2

module: stx stc-classLibrary: libbasic2

Author:

Mario Wolczko miw@cs.man.ac.uk

Description:

Occasionally you may have a block that when evaluated can be
treated as a collection -- i.e. it takes another block as parameter,
then applies that to a sequence of values.

This goodie wraps the block into an object -- an iterator -- which is
part of the collection hierarchy, and therefore inherits a variety of
useful collection-related methods.

[info:]
    NAME            Iterator
    AUTHOR          miw@cs.man.ac.uk (Mario Wolczko)
    FUNCTION        a wrapper for blocks that iterate over collections
    ST-VERSION      4.0 4.1
    PREREQUISITES   
    CONFLICTS
    DISTRIBUTION    world
    VERSION         1
    DATE    18 Jun 1991
    SUMMARY

[organisation:]
    Dept. of Computer Science   Internet:      mario@cs.man.ac.uk
    The University              uucp:        uknet!!man.cs!!mario
    Manchester M13 9PL          JANET:         mario@uk.ac.man.cs
    U.K.                        Tel: +44-61-275 6146  (FAX: 6236)
    ______the mushroom project___________________________________

Class protocol:

 on: aBlock

|i b|

b := [:whatToDo |
1 to:10 do:[:i |
whatToDo value:i
]
].

i := Iterator on:b.
i do:[:j |
Transcript showCR:j
].

usage example(s):

an iterator, simulating a collection of 100 random values: |i b| b := [:whatToDo | |rnd| rnd := Random new. 1 to:100 do:[:i | whatToDo value:(rnd next) ] ]. i := Iterator on:b. i do:[:j | j printNL ].

 on: collection msg: oneArgSelector

|i|

i := Iterator on:#(1 2 3 4 5 6 7) msg:#reverseDo:.
i do:[:j |
Transcript showCR:j
].

Instance protocol:

 identityIndexOf: anElement

Answer the identity index of anElement within the receiver.
If the receiver does not contain anElement, answer 0.

 identityIndexOf: anElement ifAbsent: exceptionBlock

Answer the identity index of anElement within the receiver.
If the receiver does not contain anElement, answer the result
of evaluating the exceptionBlock.

 indexOf: anElement

Answer the index of anElement within the receiver. If the receiver does
not contain anElement, answer 0.

 indexOf: anElement ifAbsent: exceptionBlock

Answer the index of anElement within the receiver. If the receiver does
not contain anElement, answer the result of evaluating the exceptionBlock.

 add: anObject

raises an error: Iterators are read-only

 remove: oldObject ifAbsent: anExceptionBlock

Iterators are read-only.

 removeIdentical: oldObject ifAbsent: anExceptionBlock

Iterators are read-only.

 asOrderedCollection

Answer a new instance of OrderedCollection whose elements are the elements of
the receiver. The order in which elements are added depends on the order in
which the receiver enumerates its elements. In the case of unordered collections,
the ordering is not necessarily the same for multiple requests for the conversion.

 collect: aBlock as: aClass

Reimplemented here as Iterator does not support #size.
aClass must be a non-fixed collection.

usage example(s):

(Iterator on:[:whatToDo| 'abcd' do:whatToDo]) collect:[:element | element asUppercase] as:OrderedCollection (Iterator on:[:whatToDo| 'abcd' do:whatToDo]) collect:[:element | element asUppercase] as:Array (Iterator on:[:whatToDo| '1234' do:whatToDo]) collect:[:char | char digitValue] as:ByteArray

 detectLast: aBlock ifNone: anExceptionValue

evaluate the argument, aBlock for each element in the receiver until
the block returns true; in this case return the element which caused
the true evaluation. The elements are processed in reverse order.
If none of the evaluations returns true, return the value of anExceptionValue

usage example(s):

(Iterator on:[:whatToDo| #(1 2 3 4) do:whatToDo]) detectLast:[:n | n odd] ifNone:['sorry'] (Iterator on:[:whatToDo| #(2 4 6 8) do:whatToDo]) detectLast:[:n | n odd] ifNone:['sorry']

 do: aBlock

 findFirst: aBlock ifNone: exceptionalValue

Answer the index of the first element of the receiver
for which aBlock evaluates as true.

 findLast: aBlock

Answer the index of the last element of the receiver
for which aBlock evaluates as true.

 keysAndValuesDo: aBlock

Evaluate aBlock with each of the receiver's key/value pairs
(e.g. indexes and elements) as the arguments.

 reverseDo: aBlock

evaluate the argument, aBlock for each element in reverse order.

 inspectorValueStringInListFor: anInspector
( an extension from the stx:libtool package )

returns a string to be shown in the inspector's list.
Redefined to avoid calling the iterator

 displayOn: aGCOrStream

what a kludge - Dolphin and Squeak mean: printOn: a stream;

 printOn: aStream

(comment from inherited method)
append a user readable representation of the receiver to aStream.
The text appended is not meant to be read back for reconstruction of
the receiver. Also, this method limits the size of generated string.

 block

 block: aBlock

 species

return the type of collection to be returned by collect, select etc.

 isEmpty

(comment from inherited method)
return true, if the receiver is empty

 size

(comment from inherited method)
return the number of elements in the receiver.
This is usually redefined in subclasses for more performance.

Examples:

    |i b|

    b := [:whatToDo |
              Smalltalk allClassesDo:[:cls | 
                 whatToDo value:cls
              ] 
         ].

    i := Iterator on:b.
    i do:[:cls |
       Transcript showCR:cls name
    ].

    |i b|

    b := [:whatToDo |
              Smalltalk allClassesDo:[:cls |
                 cls methodDictionary keysAndValuesDo:[:nm :mthd |
                   (nm startsWith:$a) ifTrue:[
                      whatToDo value:nm
                    ]
                 ]
              ] 
         ].

    i := Iterator on:b.
    i do:[:nm |
       Transcript showCR:nm
    ].

    |i b|

    b := [:whatToDo |
              |rnd|

              rnd := Random new.
              1 to:100 do:[:i | 
                 whatToDo value:(rnd next)
              ] 
         ].

    i := Iterator on:b.
    i do:[:j |
       j printNL
    ].

    |i b|

    b := [:whatToDo |
              |s line|

              s := 'smalltalk.rc' asFilename readStream.
              [s atEnd] whileFalse:[
                 line := s nextLine.
                 whatToDo value:line.
              ].
              s close
         ].

    i := Iterator on:b.
    i do:[:j |
       j printNL
    ].