I have an undefined method.
rb:31:in `add_song': undefined method `<<' for nil:NilClass (NoMethodError)
I do understand that #library[artist] gives nil, but I don't understand why and do not know how to fix it. Any advice?
module Promptable
def prompt(message = "What music would you like to add", symbol = ":>")
print message
print symbol
gets.chomp
end
end
class Library
attr_accessor :artist, :song
def initialize
#library = {}
end
def add_artist(artist)
#library[artist] = []
end
def add_song(song)
#library[artist] << song
end
def show
puts #library
end
end
class Artist
attr_accessor :name, :song
def initialize(artist)
#name = artist[:name]
#song = artist[:song]
end
def to_s
"#{name}, #{song}"
end
end
if __FILE__ == $PROGRAM_NAME
include Promptable
include Menu
my_library = Library.new
my_library.add_artist(Artist.new(:name => prompt("What it the artist name ?")))
my_library.add_song(Artist.new(:song => prompt("What is the song name ?")))
my_library.show
end
You're calling add_artist with one instance of Artist and add_song with another. When you look up the artist's list of songs in add_song with #library[artist] you're using a hash key (the second instance of Artist) which is not equivalent to the hash key under which you stored the list (the first instance of Artist), so you're not getting the list back, but nil.
To use two different instances of Artist as equivalent hash keys, you'll need to decide when two instances of Artist should be equal and implement eql? and hash appropriately.
Related
So when I run my lab i am getting the following error:
Associations — Song and Artist: Artist #add_song adds the song to the current artist's 'songs' collection
Failure/Error: expect(artist.songs).to include(song)
expected ["In the Aeroplane Over the Sea"] to include #<Song:0x0000000001496e88 #name="In the Aeroplane Over the Sea", #artist=#<Artist:0x0000000001496f50 #name="Neutral Milk Hotel", #songs=["In the Aeroplane Over the Sea"]>>
Diff:
## -1,2 +1,2 ##
-[#<Song:0x0000000001496e88 #name="In the Aeroplane Over the Sea", #artist=#<Artist:0x0000000001496f50 #name="Neutral Milk Hotel", #songs=["In the Aeroplane Over the Sea"]>>]
+["In the Aeroplane Over the Sea"]
But when I run my code through pry, I can see the song added into the array of the instance variable, #songs. I am working with two classes, a song class and artist class.
class Artist
attr_accessor :name
attr_reader :songs
##all = []
def initialize(name)
#name = name
save
#songs = []
end
def self.all
##all
end
def save
##all << self
end
def self.destroy_all
##all.clear
end
def self.create(name)
self.new(name)
end
def add_song(song)
if song.artist == nil
song.artist = self
end
#checks if the same song has already been added, otherwise adds new song
if #songs.include?(song.name) == false
#songs << song.name
end
binding.pry
end
end
class Song
attr_accessor :name, :artist
##all =[]
def initialize(name, artist = nil)
#name = name
#artist = artist
save
end
def self. all
##all
end
def save
##all << self
end
def self.destroy_all
##all.clear
end
def self.create(name)
self.new(name)
end
end
Your tests are expecting an aray of Song instances. But what they find is an array of strings.
To fix it you'd just need to change #songs << song.name to #songs << song.
I am sorry if I just gave you the answer instead of hinting you along to solve it yourself, but this isn't really the right platform for that kind of thing. Every question on StackOverflow can be searched by users and we want to keep things helpful to them by getting straight to the point.
However, I can give some advice. Practice reading errors. Try and understand what the error is telling you.
When I run the command I get
all the song names and then the instances following it. How do I only
get the names?
class Song
##all = []
attr_accessor :name
def initialize(name)
#name = name
##all << self
end
def self.all
##all
end
def self.print_all_song_names
##all.each do |song|
puts song.name
end
end
end
hotline_bling = Song.new("Hotline Bling")
thriller = Song.new("Thriller")
ninety_nine_problems = Song.new("99 Problems")
thriller = Song.new("Thriller")
puts Song.print_all_song_names
Which outputs:
Hotline Bling
Thriller
99 Problems
Thriller
#<Song:0x00000000058ced30>
#<Song:0x00000000058cecb8>
#<Song:0x00000000058cebc8>
#<Song:0x00000000058ceb50>
The issue with your code is your calling puts here and there.
The code already calls puts in print_all_song_names, and after you call puts Song.print_all_song_names which roughly means call the method and print the value returned.
each returns a receiver, which means print_all_song_names returns the value of ##all class variable. Which gets printed again.
To fix it, just don’t call puts in the last line; Song.print_all_song_names already prints out everything needed.
Song.print_all_song_names # voilà
Below is a program that implements a tree.
class Tree
attr_accessor :children, :node_name
def initialize(name_children=[])
#children = children
#node_name = name
end
def visit_all(&block)
visit &block
children.each {|c| c.visit_all &block}
end
def visit(&block)
block.call self
end
end
ruby_tree = Tree.new( "Ruby", [Tree.new("Reia"), Tree.new("MacRuby")] )
puts "Visiting a node"
ruby_tree.visit {|node| puts node.node_name}
puts
puts "visiting entire tree"
ruby_tree.visit_all {|node| puts node.node_name}
When I run this code it errors at this line
ruby_tree = Tree.new( "Ruby", [Tree.new("Reia"), Tree.new("MacRuby")] )
The error I'm receiving is
tree.rb:6:in `initialize': undefined local variable or method `name' for #<Tree:0x007f94020249f8 #children=nil> (NameError)
from tree.rb:19:in `new'
from tree.rb:19:in `<main>'
Any help would be awesome.
You have a typo in your initialize method accepts a single argument named name_children, but from the body of that method it looks like the underscore should have been a comma - name, children.
Here's the problem - line 6 #node_name = name. Where do you define that variable?
In your constructor, (initialize), why aren't you entering the variables children, and name as such instead of a children_name ? What it seems to me is that when you are trying to instantiate the class by creating the objects, when it goes to the initialize constructor, it does not find a name in there.
def initialize(name, children=[])
#children = children
#node_name = name
en
As you have define attr_accessor :name in your Model so there you have to define Children method in you model like as
def self.name
# here will be you code which you want
end
trying to pick up ruby through this programming ruby site and i'm stuck on this syntax
class SongList
def initialize
#songs = Array.new
end
def append(aSong)
#songs.push(aSong)
self
end
def deleteFirst
#songs.shift
end
def deleteLast
#songs.pop
end
end
When i go to add a song...
list = SongList.new
list.append(Song.new('title1', 'artist1', 1))
I get this error message:
NameError: uninitialized constant Song ...Programming Ruby
I saw that i need to require the variable Song, but I'm not sure where to do it within the SongList class....
You can use Ruby Struct class :
A Struct is a convenient way to bundle a number of attributes together, using accessor methods, without having to write an explicit class.
class SongList
def initialize
#songs = [] # use [] instead of Array.new
end
def append(aSong)
#songs.push(aSong)
self
end
def delete_first
#songs.shift
end
def delete_last
#songs.pop
end
end
Song = Struct.new(:song_name, :singer, :var)
list = SongList.new
list.append(Song.new('title1', 'artist1', 1))
# => #<SongList:0x9763870
# #songs=[#<struct Song song_name="title1", singer="artist1", var=1>]> var=1>]>
So, I know there is a simple error, but I just can't seem to spot it. I'm using Modules/Mixins for the first time and any help would be much appreciated. I keep getting this error:
undefined method `this_is' for Value:Module (NoMethodError)
But it looks like the method is there...Here are is my module and classes...
module Value
def this_is
puts "#{self.players_hand} is the players hand"
end
end
require './value.rb'
class Player
include Value
attr_accessor :players_hand
def initialize
#players_hand = 0
end
def value_is
Value.this_is
end
end
require './player.rb'
class Game
def initialize
#player = Player.new
end
def start
puts #player.players_hand
puts #player.value_is
end
end
game = Game.new
game.start
When you include Value inside of the Player class, you are making the Value module's methods a part of the Player class, so the this_is method is not namespaced. Knowing that, we need to change this method:
def value_is
Value.this_is
end
To:
def value_is
this_is
end