1 "{ Package: 'stx:libbasic2' }"

     2 

     3 Stream subclass:#SelectingReadStream

     4 	instanceVariableNames:'selectBlock hasReadAhead readAhead inStream'

     5 	classVariableNames:''

     6 	poolDictionaries:''

     7 	category:'Streams'

     8 !

     9 

    10 !SelectingReadStream class methodsFor:'documentation'!

    11 

    12 documentation

    13 "

    14     A stream which only delivers elements for which a select block returns true

    15     from an underlying stream. 

    16 

    17     Needs readAhead for proper atEnd handling.

    18 

    19     [instance variables:]

    20         hasReadAhead        - because nil is a valid read-element,

    21                             this is used to know if readAhead is valid.

    22 "

    23 !

    24 

    25 examples

    26 "

    27     |s|

    28 

    29     s := SelectingReadStream 

    30             on:#(1 2 3 4 5 6 7 8) readStream

    31             selecting:[:each | each even].

    32     s upToEnd  

    33 "

    34 ! !

    35 

    36 !SelectingReadStream class methodsFor:'instance creation'!

    37 

    38 on:aStream selecting:aBlock

    39     ^ self basicNew on:aStream selecting:aBlock

    40 ! !

    41 

    42 !SelectingReadStream methodsFor:'instance creation'!

    43 

    44 on:aStream selecting:aBlock

    45     inStream := aStream.

    46     selectBlock := aBlock.

    47     hasReadAhead := false.

    48 ! !

    49 

    50 !SelectingReadStream methodsFor:'queries'!

    51 

    52 atEnd

    53     |el|

    54 

    55     hasReadAhead ifTrue:[^ false].

    56 

    57     [

    58         inStream atEnd ifTrue:[

    59             ^ true

    60         ].

    61         el := inStream next.

    62         (selectBlock value:el)

    63     ] whileFalse.

    64     readAhead := el.

    65     hasReadAhead := true.

    66     ^ false.

    67 ! !

    68 

    69 !SelectingReadStream methodsFor:'reading'!

    70 

    71 next

    72     |el|

    73     

    74     hasReadAhead ifTrue:[

    75         hasReadAhead := false.

    76         ^ readAhead

    77     ].

    78     [

    79         inStream atEnd ifTrue:[

    80             ^ self pastEndRead

    81         ].

    82         el := inStream next.

    83         (selectBlock value:el)

    84     ] whileFalse.

    85     ^ el

    86 ! !

    87 

    88 !SelectingReadStream class methodsFor:'documentation'!

    89 

    90 version_CVS

    91     ^ '$Header: /cvs/stx/stx/libbasic2/SelectingReadStream.st,v 1.1 2009-12-05 11:15:39 cg Exp $'

    92 ! !