Class: Lazy

• Inheritance
• Description
• Instance protocol
  • evaluating
  • printing
  • synchronising
  • testing
• Examples

Inheritance:

   ProtoObject
   |
   +--Lazy

Package:

stx:libbasic2

Category:

Kernel-Processes

Version:

rev: 1.19 date: 2021/01/20 15:56:36

user: cg

file: Lazy.st directory: libbasic2

module: stx stc-classLibrary: libbasic2

Description:

I represent an execution which may or may not be required.
I will not start execution until at least one message has been received.
The messages sent to me are delayed until execution has completed.

copyright
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         written consent of the author(s).
Further information on the copyright conditions may be obtained by
sending electronic mail:
       To: goodies-lib@cs.man.ac.uk
       Subject: copyright
or by writing to The Smalltalk Goodies Library Manager, Dept of
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(C) Copyright 1992 University of Manchester
For more information about the Manchester Goodies Library (from which
this file was distributed) send e-mail:
       To: goodies-lib@cs.man.ac.uk
       Subject: help

Instance protocol:

 block: aBlock

Execute aBlock in parallel, but ensure that any messages sent
to me before execution of the block has terminated are
suspended until it has terminated. Do not start the evaluation
until at least one message has been sent to the receiver.

 block: aBlock value: aValue

Execute aBlock in parallel, but ensure that any messages sent
to me before execution of the block has terminated are
suspended until it has terminated. Do not start the evaluation
until at least one message has been sent to the receiver.

 block: aBlock value: value1 value: value2

Execute aBlock in parallel, but ensure that any messages sent
to me before execution of the block has terminated are
suspended until it has terminated. Do not start the evaluation
until at least one message has been sent to the receiver.

 block: aBlock value: value1 value: value2 value: value3

Execute aBlock in parallel, but ensure that any messages sent
to me before execution of the block has terminated are
suspended until it has terminated. Do not start the evaluation
until at least one message has been sent to the receiver.

 block: aBlock valueWithArguments: anArray

Execute aBlock in parallel, but ensure that any messages sent
to me before execution of the block has terminated are
suspended until it has terminated. Do not start the evaluation
until at least one message has been sent to the receiver.

 displayOn: aGCOrStream

notice: displayString and displayOn: will not wait for the value (they are for developers and inspectors),
whereas printString and printOn: will wait (they are for the program to print data).

 displayString

notice: displayString and displayOn: will not wait for the value (they are for developers and inspectors),
whereas printString and printOn: will wait (they are for the program to print data).

 _evaluate_

answer the computed value

 doesNotUnderstand: aMessage

Any message to a Lazy will end up here.

 perform: aSelector withArguments: argArray

send the message aSelector with all args taken from argArray
to the receiver.

 isLazyValue

true if I have no value yet
(i.e. would block when sending me a message)

Examples:

  | fac |
  fac := [100 factorial] lazyValue.
  Transcript showCR: 'Doing nothing. '.
  (Delay forSeconds: 2) wait.
  Transcript showCR: fac printString.

  | fac1 fac2 |
  fac1 := [Transcript showCR: 'Starting fac1.. '. 100 factorial] lazyValue.
  fac2 := [Transcript showCR: 'Starting fac2.. '. 120 factorial] lazyValue.
  fac2 value.
  fac1 value.
  Transcript showCR: 'both completed.'.

  | temp |
  temp := [:x :y :z | x * y * z] lazyValueWithArguments: #(2 3 4).
  Transcript  showCR: temp printString.