CODEWITHSUNDEEP
ruby-on-railsrubyruby-on-rails-3
Ben2pop
Ben2pop

Reputation: 756

Ruby code understanding - From code School

) I am learning ruby via the very good website code School, however in one of their examples I do not understand the method and the logic behind, could someone explain me ?

Thank you so much ;-)

Here is the code 

search = "" unless search 
games = ["Super Mario Bros.", "Contra", "Metroid", "Mega Man 2"]
matched_games = games.grep(Regexp.new(search))
puts "Found the following games..."
matched_games.each do |game|
  puts "- #{game}"
end

I do not really understand line 1 and 3 

search = "" unless search 

matched_games = games.grep(Regexp.new(search))

Upvotes: 0

Views: 206

Answers (3)

hedgesky
hedgesky

Reputation: 3311

Search should be instance of Regexp or nil. In first line search is setting to blank string if it's equal to nil initially.

In third string matched_games is setting to array of strings matched to given regex (http://ruby-doc.org/core-2.0/Enumerable.html#method-i-grep)

Upvotes: 0

vee
vee

Reputation: 38645

The following statement assigns empty string to search variable if search is not defined. 

search = "" unless search

Had this assignment not be done, Regexp.new would have thrown an TypeError with message no implicit conversion of nil into String, or if search was not defined then NameError with message undefined local variable or method 'search'...

In the following statement: 

matched_games = games.grep(Regexp.new(search))

games.grep(pattern) returns an array of every element that matches the pattern. For further details please refer to grep. Regexp.new(search) constructs a new regular expression from the supplied search variable which can either be a string or a regular expression pattern. Again, for further details please reference Regexp::new

So say for example search is "" (empty string), then Regexp.new(search) returns //, if search = 'Super Mario Bros.' then Regexp.new(search) returns /Super Mario Bros./.

Now the pattern matching: 

# For search = "", or Regexp.new(search) = //
matched_games = games.grep(Regexp.new(search))
Result: matched_games = ["Super Mario Bros.", "Contra", "Metroid", "Mega Man 2"]

# For search = "Super Mario Bros.", or Regexp.new(search) = /Super Mario Bros./
matched_games = games.grep(Regexp.new(search))
Result: matched_games = ["Super Mario Bros."]

# For search = "something", or Regexp.new(search) = /something/
matched_games = games.grep(Regexp.new(search))
Result: matched_games = []

Hope this makes sense.

Upvotes: 1

Billy Chan
Billy Chan

Reputation: 24815

vinodadhikary said all. I just don't like the syntax OP mentioned

search = "" unless search

This is nicer 

search ||= ""

Upvotes: 0

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