Since I switch between languages a fair amount I find it hard to keep track of each’s idiosyncrasies in common constructs. Presently I shall briefly note AS3′s implementation of Dictionaries, Arrays and Objects and differences therein:

Object

• Maps String keys to Object values.
• Features the convenience constructor {}
• Access members with brackets or dots. Dots convert the argument into a String literal. For example:
  
  var bobby_b:String = "cello";
  var arrgh:Array = [];
  arrgh[bobby_b] = "uhn"; //equivalent to arrgh["cello"] = "uhn";
  arrgh.bobby_b = "yeah"; //equivalent to arrgh["bobby_b"] = "yeah";

  //post condition:

  arrgh["cello"] => "uhn"
arrgh["bobby_b"] => "yeah"


• Can lift (press) 10 tons

Array

• Are actually associative arrays, as expected, so no speed benefit there.
• Equivalent to Object. One might go so far as to say they are identical, if one was confident in this, but sadly one is not.
• Feature the convenience constructor []
• Probably semantically advantageous over Objects where strict lists will be used.

Dictionary

• Maps Object keys to Object values
• Can use Array syntax for addressing
• Has no convenience constructor
• Must be imported from flash.utils
• for…in loops don’t understand Object keys – it always expects Strings – so one must cast the key to the desired type to avoid compiler errors:
  
for (var key in new_edition){
var member:Musician = key;
// proceed with your life
}


  NOT:

  
for (var key:Musician in new_edition) { ... } //compiler error "Implicit coercion of a value of type String to an unrelated type Musician"


  OR:

  
for (var key:Object in new_edition) { ... } //compiler error "implicit coercion of etc"


  BUT MAYBE:

  
for (var key:* in new_edition){ ...}


  AND ALSO:

  
for (var key in new_edition){
key = key as Musician;
// do whatever
}


  AND ALSO MAYBE:

  
for (var key in new_edition){
//and just don't even bother with the cast, they'll figure it out
}


  That last one is nice for typing, but not nice for typing, if you take my meaning. Kinda defeats the purpose of the kinda-type system they so painstakingly (?) crafted. Recommendation: use the first form with an explicit cast and an extra variable so you get the benefit of the compiler.

• Cannot by typed correctly by me on the first try. I always write “Dicionary”. Can’t stop.