Learn Ruby the Hard Way #41 [closed] - ruby

Question

Closed. This question needs details or clarity. It is not currently accepting answers.
Want to improve this question? Add details and clarify the problem by editing this post.
Closed 8 years ago.
Improve this question
Hi I`m learning from LRtHW and I got stuck....
I have program like this:
require 'open-uri'
WORD_URL = "http://learncodethehardway.org/words.txt"
WORDS = []
PHRASES = {
"class ### < ###\nend" => "Make a class named ### that is-a ###.",
"class ###\n\tdef initialize(###)\n\tend\nend" => "class ### has-a initialize that takes ### parameters.",
"class ###\n\tdef ***(###)\n\tend\nend" =>"class ### has-a function named *** that takes ### parameters.",
"*** = ###.new()" => "Set *** to an instance of class ###.",
"***.***(###)" => "From *** get the *** function, and call it with parameters ###.",
"***.*** = '***'" => "From *** get the *** attribute and set it to '***'."
}
PHRASE_FIRST = ARGV[0] == "english"
open(WORD_URL) do |f|
f.each_line {|word| WORDS.push(word.chomp)}
end
def craft_names(rand_words, snippet, pattern, caps=false)
names = snippet.scan(pattern).map do
word = rand_words.pop()
caps ? word.capitalize : word
end
return names * 2
end
def craft_params(rand_words,snippet,pattern)
names = (0...snippet.scan(pattern).length).map do
param_count = rand(3) + 1
params = (0...param_count).map {|x| rand_words.pop()}
params.join(', ')
end
return names * 2
end
def convert(snippet, phrase)
rand_words = WORDS.sort_by {rand}
class_names = craft_names(rand_words, snippet, /###/, caps=true)
other_names = craft_names(rand_words, snippet,/\*\*\*/)
param_names = craft_params(rand_words, snippet, /###/)
results = []
for sentence in [snippet, phrase]
#fake class name, also copies sentence
result = sentence.gsub(/###/) {|x| class_names.pop}
#fake other names
result.gsub!(/\*\*\*/) {|x| other_names.pop}
#fake parameter list
result.gsub!(/###/) {|x| param_names.pop}
results.push(result)
end
return results
end
# keep going until they hit CTRL-D
loop do
snippets = PHRASES.keys().sort_by { rand }
for snippet in snippets
phrase = PHRASES[snippet]
question, answer = convert(snippet, phrase)
if PHRASE_FIRST
question, answer = answer, question
end
print question, "\n\n> "
odp = gets.chomp
if odp == "exit"
exit(0)
end
#exit(0) unless STDIN.gets
puts "\nANSWER: %s\n\n" % answer
end
end
I understand most of this code, but I have a problem with:
for sentence in [snippet, phrase]
I know that it is a "for" loop and it creates a "sentence" variable, but how does the loop know that it need to look in a key and value of hash "PHRASES"
And my second "wall" is:
question, answer = convert(snippet, phrase)
It looks like it creates and assigns "question" and "answer variables to the "convert" method with "snippet" and "phrase" parameters... again how does it assigns "question" to a key and answer to a value.
I know that this is probably very simple but as for now it blocks my mind :(

Answer 1

For your first question about the for-loop:
Look at where the for-loop is defined. It's inside the convert() method, right? And the convert() method is passed two arguments: one snippet and one phrase. So the loop isn't "looking" for values in the PHRASES hash, you are the one supplying it. You're using the method's arguments.
For your second question about assignment:
In Ruby we can do something called "destructuring assignment". What this means is that we can assign an array to multiple variables, and each variable will hold one value in the array. That's what's happening in your program. The convert() method returns a two-item array, and you're giving a name (question and answer) to each item in the array.
Here's another example of a destructuring assignment:
a, b, c = [1, 2, 3]
a # => returns 1
b # => returns 2
c # returns 3
Try this out in IRB and see if you get the hang of it. Let me know if I can help clarify anything, or if I misunderstood your question. You should never feel bad about asking "simple" questions!