Loops

Loops

• Loops are expressed as messages
• Many different ones
  • Plain loops
  • Conditional loops
• Messages sent to numbers, collections or blocks
• Iterators

Loops: timesRepeat:

To repeat a given number of times an action

	4 timesRepeat: [ self doSomething ]

Loops: to:do:

1 to: 100 do:
    [ :i | ... i ... ]

to:do: is a method defined on Number

Example: to:do:

The block is executed with the temporary i taking values from 1 to 100

1 to: 100 do:
    [ :i | Transcript show: i ; space ]

Loops: to:by:do:

    0 to: 100 by: 3 do: [ :i | ... i ... ]

to:by:do: is also a method defined on Number

Example: to:by:do:

The block is executed with i taking values from 1 to 100 by step of 3

1 to: 100 by: 3 do:
    [ :i | Transcript show: i ; space ]

Basic Iterators Overview

• do: (iterate)
• collect: (iterate and collect results)
• select: (select matching elements)
• reject: (reject matching elements)
• detect: (get first element matching)
• detect:ifNone: (get first element matching or a default value)
• includes: (test inclusion)
• and a lot more...

Loops: do:

    aCol do: [ :each | ... ]

The block is executed with each taking as value all the elements of aCol

Example: The iterator do:

#(15 10 19 68) do:  
      [:i | Transcript show: i ; cr ]

Loops: whileTrue:

    [ ... ] whileTrue: [ ... ]

Executes the argument, aBlock, as long as the value of the receiver is true

Color >> atLeastAsLuminentAs: aFloat 
  | revisedColor |
  revisedColor := self.
  [ revisedColor luminance < aFloat ] 
     whileTrue: [ revisedColor := revisedColor slightlyLighter ].
  ^ revisedColor

Loops: whileTrue

Executes the receiver, as long as its value is true

    [ ... ] whileTrue

Equivalent with whileFalse and whileFalse:

Summary

• Loops are expressed as messages
• Many different ones
  • Plain loops
  • Conditional loops
• Messages sent to numbers, collections or blocks
• Iterators