Reading: Tate, Section 2.3 (Floating Down From The Sky)
Please submit a question by 9 p.m. on {$thu01}.
Questions I've answered
On page 43, in the definition of initialize there is children=[], is this just saying that children is an array?
Yes.
Why does the following not work?
{puts 'Hello, World!'}.call
Because functions are not quite first-class values in Ruby (at least
from my perspective). They are not treated the same way other values are
treated.
I do not quite understand the class hierarchy as explain by Tate on
pages 41 and 42 in the part titled "Defining Classes." I am particularly
confused about the meaning of 4.class.class. Could we go
over the class hierarchy in class (pun intended)?
Yes.
Can we talk more about what a mixin is?
Yes.
What are some other practical uses of symbols :keyword in Ruby?
The most obvious use is in hashes that simulate named parameters.
Why is Ruby not able to sort keys start with ":" in a hash?
Because symbols in Ruby are atomic
, just like symbols in
Scheme. They are not supposed to represent strings. They are, instead,
mnemonics that can be quickly compared for equality.
I'm still a bit confused about duck typing. In this section's example
of duck typing, Tate writes, The module interacts with the including
class at an intimate level. The module will often depend on several class
methods. With Java, this contract is explicit: the class will implement
a formal interface. With Ruby, this contract is implicit, through duck
typing.
So I guess the difference is that Java wouldn't even compile
if there was a chance that a method were being used by an object that
didn't have that method defined. But Ruby doesn't compile,
so
the difference seems to stem from - or even reduce to - Ruby's doing
everything at runtime. Is this so?
It's a bit more complex than that. Ruby could still require you to
specify the expected type of a parameter to a function and verify that
the paremeter had that type (or included that mixin or ...). But Ruby
delays the question until you try to do something with the object, even
in executing code.
What does yield do in Ruby?
Yields control to the code block associated with the current thing.
Potential discussion questions
Why does Ruby use an end keyword instead of using whitespace or brackets?
Would it always be beneficial to add comparable and enumerable mixins
to our classes whenever possible?
Why doesn't Ruby support named parameters? It seems like having them
would provide programmers with some syntactic sugar (which seems like
a pretty important factor to Ruby's designer).
Questions I have not yet answered
Can you explain or give an example of when to prepend a variable with
@ and when to prepend a variable with @@?
It appears that using the & syntax one can pass blocks
around at will. How does this work if blocks aren't objects? Is the
interpreter just saving the code snippet behind the scenes?
Why is inject called inject? It sounds a lot like fold. Is the name inject preferred by any other languages?
Is there a way to force an object/class to be a singleton?
Can you explain the relationship between objects, classes, and modules?
What are the advantages / disadvantages of using modules instead of interfaces?
The attr_accessor keyword supposedly creates an accessor
and a getter, which seem to be simply 'variable' and 'variable='. In
other OO languages I was told to always leave variables private and
use accessors/mutators to access and modify them. Why does Ruby not use
this idea? (or is there some way to define the accessors and mutators
explicitly?)