Class: True

• Inheritance
• Description
• Instance protocol
  • Javascript support
  • conditional evaluation
  • converting
  • debugging
  • inspecting
  • logical operations
  • printing & storing

Inheritance:

   Object
   |
   +--Boolean
      |
      +--True

Package:

stx:libbasic

Category:

Kernel-Objects

Version:

rev: 1.42 date: 2022/03/16 13:28:01

user: stefan

file: True.st directory: libbasic

module: stx stc-classLibrary: libbasic

Description:

True has only one instance, true, representing logical truth.

Some methods are implemented here and in False, instead of the common
superclass Boolean. This has the advantage that no truth-value checks
are needed, but instead the truth check is done in the method lookup.
However, remember that some messages to booleans are inline coded in
the compilers (both interpreted and machine code). Therefore redefinition
of some methods here will not have any effect on compiled code.
(redefining ifTrue: to something else will probably crash the smalltalk
 world anyway ...)

copyright
COPYRIGHT (c) 1988 by Claus Gittinger
             All Rights Reserved

This software is furnished under a license and may be used
only in accordance with the terms of that license and with the
inclusion of the above copyright notice.   This software may not
be provided or otherwise made available to, or used by, any
other person.  No title to or ownership of the software is
hereby transferred.

Instance protocol:

 js_not
( an extension from the stx:libjavascript package )

 and: aBlock

evaluate aBlock if the receiver is true.
since the receiver is known to be true,
return the value of evaluating the block.
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 and: block1 and: block2

evaluate block1 if the receiver is true,
if that is also true, return the result from block2.
Notice:
This method may be open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 and: block1 and: block2 and: block3

evaluate block1 if the receiver is true,
if that is also true, evaluate block2.
if that is also true, return the result from block3.
Notice:
This method may be open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 and: block1 and: block2 and: block3 and: block4

evaluate block1 if the receiver is true,
if that is also true, evaluate block2.
if that is also true, evaluate block3.
if that is also true, return the result from block4.
Notice:
This method may be open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 ifFalse: aBlock

If the receiver is false, return the value of evaluating aBlock; nil otherwise.
Since the receiver is definitely true here, unconditionally return nil value.
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 ifFalse: falseBlock ifTrue: trueBlock

return the value of evaluating trueBlock (since the receiver is true)
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 ifTrue: aBlock

If the receiver is true, return the value of evaluating aBlock; nil otherwise.
Since the receiver is definitely true here, unconditionally return the block's value.
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 ifTrue: trueBlock ifFalse: falseBlock

return the value of evaluating trueBlock (since the receiver is true)
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 or: aBlock

evaluate aBlock if the receiver is false.
since the receiver is known to be true simply return true.
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 or: block1 or: block2

evaluate block1... if the receiver is false.
since the receiver is known to be true simply return true.
Notice:
This method may be open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 or: block1 or: block2 or: block3

evaluate block1... if the receiver is false.
since the receiver is known to be true simply return true.
Notice:
This method may be open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 or: block1 or: block2 or: block3 or: block4

evaluate block1... if the receiver is false.
since the receiver is known to be true simply return true.
Notice:
This method may be open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 asInteger

false->0; true->1

 asNumber

false->0; true->1

 haltIfFalse

halt if the receiver is false

 haltIfTrue

halt if the receiver is true

Usage example(s):

3 haltIfNil nil haltIfNil true haltIfTrue false haltIfFalse

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

returns the icon to be shown alongside the value list of an inspector

 & aBoolean

return true if both the receiver and the argument are true
(since the receiver is true, return the argument, aBoolen)
Notice:
as this is a binary message, the argument is always evaluated.
It might be better to use and:[...], which does not evaluate
the argument if the receiver is already false.

 ==> aBoolean

same as implies:
return true if receiver implies the argument

 eqv: aBoolean

return true if both the receiver and the argument are the same truth value
(since the receiver is true, return true if the argument is also)

 implies: aBoolean

return true if receiver ==> argument.
That is: if a is true, b must be true; if a is false, b can be any

 not

return true if the receiver is false, false otherwise
(since the receiver is true, return false).
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 xor: aBoolean

return true if the receiver and the argument are different truth values
(since the receiver is true, return true, if the argument is not)

 | aBoolean

return true if either the receiver or the argument are true
(since the receiver is true, return true).
Notice:
as this is a binary message, the argument is always evaluated.
It might be better to use or:[...], which does not evaluate
the argument if the receiver is already true.

 printString

return character sequence representing the receiver