Understanding the Implementation of ifTrue:ifFalse:

Yes ifTrue:ifFalse: is a message!

Weather isRaining
    ifTrue: [ self takeMyUmbrella ]
    ifFalse: [ self takeMySunglasses ]

• Conceptually ifTrue:ifFalse: is a message sent to an object: a boolean!
• Heavily optimised by the compiler

Exercise

• Propose an implementation of ifTrue:ifFalse:
• You only have objects, messages and closures

   false ifTrue: [ 3 ] ifFalse: [ 5 ]
   -> 5

   true ifTrue: [ 3 ] ifFalse: [ 5 ]
   -> 3

Implementing ifTrue:ifFalse:

• Remember:
  • [ ] freezes body execution
  • value kicks execution of a frozen code
• How to implement ifTrue:ifFalse:?
• Remember Not and Or?

Implementation of ifTrue:ifFalse:

Let the receiver decide!

True >> ifTrue: aTrueBlock ifFalse: aFalseBlock
   ^ aTrueBlock value

False >> ifTrue: aTrueBlock ifFalse: aFalseBlock
   ^ aFalseBlock value

Implementation of ifTrue:ifFalse:

Conclusion

• Sending a message selects the right method
• Let the receiver decide
• [ ] freezes computation and value forces execution