questions.txt

Please Read The Chapters on: 
Containers, Blocks, and Iterators 
Sharing Functionality: Inheritance, Modules, and Mixins

1. What is the difference between a Hash and an Array?

An array is an object that holds a collection of object references, 
with a non-negative integer position for each element serving as that
object's index. For example:

a = [ 1, 3, 5 ]
a[0] # => 1
a[1] # => 3
a[2] # => 5

A hash is also an object that holds a collection of object references, but
each element is indexed with a provided key. Keys can be any object type:
strings, symbols, etc. For example:

petsounds = { dog: 'woof', cat: 'meow', bird: 'chirp' }

petsounds['cat'] # => 'meow'

2. When would you use an Array over a Hash and vice versa?

Arrays can be readily used as stacks and queues, and have built-in methods
to support stack/queue types of operations like adding or removing elements
from the stack (e.g., push, pop). 

Hashes are mainly useful because of their ability to be indexed by anything 
besides integers. Also, hash enumerations occur in the order in which
elements were added to the hash, which could also be useful for tracking
duration of collection membership.

3. What is a module? Enumerable is a built in Ruby module, what is it?

A module is a way of grouping together methods, classes, and constants,
with two major benefits:

 a. namespaces (prevent method and/or constant name clashes)
 b. supports use of mixins, which results when a module is included in
    a class definition such that all the module's instance methods are
    immediately available to the containing class

Enumerable is a module that allows for the use of collection class methods
(e.g., map, include?, find_all?) to be available to the class containing
the Enumerable module. Effectively, you can create a class that uses
enumerative methods found in Arrays and Hashes by simply creating an iterator
called "each" (which leverages the each method from the host class). 

4. Can you inherit more than one thing in Ruby? How could you get around this problem?

Yes. The use of modules and mixins can help prevent inheritance issues due to 
method name clashes, where the same class method variable name may exist in multiple
classes within a program. Also, a mixin is vulnerable to instance variable
name clashes with other mixins or their host class. If unique instance 
variable names are used in a mixin relative to those elsewhere, clashes can
be avoided (or perhaps use a hash in the module indexed by current objectID).

5. What is the difference between a Module and a Class?

A module cannot have instances (i.e., they do not have their own state), 
but can be included in a class such that its instance methods become 
instantly available to the class. Mixed-in modules act essentially as 
superclasses.