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Class: True


Inheritance:

   Object
   |
   +--Boolean
      |
      +--True

Package:
stx:libbasic
Category:
Kernel-Objects
Version:
rev: 1.37 date: 2019/03/13 09:31:51
user: cg
file: True.st directory: libbasic
module: stx stc-classLibrary: libbasic
Author:
Claus Gittinger

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 ...)


Related information:

    False

Instance protocol:

Javascript support
o  js_not
( an extension from the stx:libjavascript package )

conditional evaluation
o  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.

o  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.

o  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.

o  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.

o  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.

o  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.

o  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.

o  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.

o  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.

o  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.

o  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.

o  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.

converting
o  asInteger
false->0; true->1

o  asNumber
false->0; true->1

debugging
o  haltIfFalse
halt if the receiver is false

o  haltIfTrue
halt if the receiver is true

usage example(s):

     3 haltIfNil
     nil haltIfNil
     
     true haltIfTrue
     false haltIfFalse

inspecting
o  inspectorValueListIconFor: anInspector
( an extension from the stx:libtool package )
returns the icon to be shown alongside the value list of an inspector

logical operations
o  & 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.

o  ==> aBoolean
same as implies:
return true if receiver => argument

o  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)

o  implies: aBoolean
return true if receiver => argument

o  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.

o  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)

o  | 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.

printing & storing
o  printString
return character sequence representing the receiver



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