Dynamic Vs. Literal Arrays

What You Will Learn

• Literal arrays are not created using messages
• Dynamic arrays are created at runtime using messages
• Still they are all instances of Array

Remember: Literal Arrays

Literal array definition can only contain objects that have a textual (literal) representation: numbers, strings, nil, symbols, boolean

#(45 'milou' 1300 true #tintin)
> #(45 'milou' 1300 true #tintin)

Literal arrays are instances of the class Array

#(45 38 1300 8) class
> Array

Literal/Dynamic Arrays

A literal array

#(45 38 'milou' 8) 
> #(45 38 'milou' 8) 

A dynamic array

Array with: 45 with: 38 with: 'milou' with: 8
> #(45 38 'milou' 8) 

Both are Array instances

Dynamic Array Compact Syntax

Defining dynamic arrays is tedious

| array | 
array := (Array new: 2). 
array 
    at: 1 put: 10 @ 10 ; 
    at: 2 put: (Point x: 100 y: 200).
array

{ expression1 . expression2 } is syntactic sugar to create dynamic arrays

{(10@20) . (100@200)}
{Point x: 10 y: 20 . Point x: 100 y: 200}

Literal Array Creation Time

Literal arrays are created at compile time by the parser when the expression is read and not during the execution

| a |
a := 12.
#(a + 1 . 13) 
> #(#a #+ 1 #'.' 13)

Dynamic arrays execute expressions

| a |
a := 12.
{a + 1 . 13} 
> #(13 . 13)

Literal vs. Dynamic

{} executes expressions while #() not

{(10@20) . (10@20)}
> {(10@20) . (10@20)}

#((10@20) . (10@20))
> #(#(10 #@ 20) #'.' #(10 #@ 20))

{(10@20) . (10@20)} size 
> 2

#((10@20) . (10@20)) size 
> 3

Nested Arrays

() inside a literal array produces a nested literal array

#((10@20) (100@200))
> #(#(10 #@ 20) #(100 #@ 200))

#((10@20) . (100@200)) first
> #(10 #@ 20)

Summary

• Only one kind of Arrays
• Three ways
  • Literal syntax: #( ) (no message)
  • Using messages Array new: 3
  • Syntactic sugar: Dynamic { . . }