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What is wrong with this code?
class Person
def initialize(name)
#name = name
end
def greet(other_name)
"Hi #{other_name}, my name is #{name}"
end
end
Write the code as
class Person
def initialize(name)
#name = name
end
def greet(other_name)
"Hi #{other_name}, my name is #{#name}" # <~~ you missed `#` before name.
end
end
If you write only name(instead of #name), Ruby will try to look for a local var named as name, but you didn't define any. Then it will try to check if any method you have defined as name or not, that also not present. So finally you will get
undefined local variable or method `name'
Here is an example after the fix :
#!/usr/bin/env ruby
class Person
def initialize(name)
#name = name
end
def greet(other_name)
"Hi #{other_name}, my name is #{#name}"
end
end
Person.new("Raju").greet('Welcome!') # => "Hi Welcome!, my name is Raju"
Related
This question already has answers here:
Instance variable: self vs #
(6 answers)
Closed 5 years ago.
I have a question about what the best way is to reference a class variable in Ruby.
Here is a class I made:
class Person
attr_accessor :name
def initialize(name)
#name = name
end
def say_name
puts #name
end
def say_name2
puts self.name
end
end
bob = Person.new("Bob")
bob.say_name
=> "Bob"
bob.say_name2
=> "Bob"
Both of the "say_name" methods seems to work as intended. Why use the #variable vs the self.variable??
attr_accessor :name just creates method name, which returns #name variable, something like
def name
#name
end
instead of you.
Without attr_accessor both self.name and name will not work and return NoMethodError.
#name will work in all cases.
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"In my example, the initialize method expects to receive the two arguments. Once you associate an argument with the initialize method, you can not leave it off. If you do, it will generate an error." - so much for the theory but in my case it is the opposite ;(
class Player
attr_accessor :name, :age, :score
def inicialize(name, age, score)
#name = name
#age = age
#score = score
end
def to_s
"Player #{name} is #{age} old and have #{score} points"
end
end
So I call it simply:
player = Player.new("Name", "Surname", 25)
but the compiler responds:
`initialize': wrong number of arguments (given 3, expected 0) (ArgumentError)
So, than I do:
player = Player.new; player.name = 'Peter'
and it works.... why?
When I delete the arguments of inicialize it is the same exact story.
it should be initialize, not inicialize.
class Player
attr_accessor :name, :age, :score
def initialize(name, age, score)
#name = name
#age = age
#score = score
end
def to_s
"Player #{name} is #{age} old and have #{score} points"
end
end
player = Player.new("Name", "Surname", 25)
#=> #<Player:0x007fca2a4dfbb0 #age="Surname", #name="Name", #score=25>
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How can I make a class that makes multiple classes. I have this:
class Person
attr_accessor :name
#name = name
def initialize
Person.new
Person.new
Person.new
Person.new
Person.new
Person.new
Person.new
Person.new
end
end
but that returns stack level to deep.
I wasn't clear where you wanted to get the names from -- External file? Manual Input? Database?
In any case, you could probably do something like:
class Person
attr_accessor :name
def initialize(name)
self.name = name
end
end
##some sort of input goes here and creates the array of names
arrayofnames = [name1,name2,name3]
arrayofnames.each do |person|
Person.new(person)
end
As part of the same enumeration you could put each new person into an array or store them somewhere else for later use. Here I built the class and added the people to it separately, although you could probably build the same enumeration into the class itself.
Hope that helps,
The problem that you are facing is that you are creating a person which in turn is creating 10 other person objects which are all returning 10 person objects. This continues on indefinitely.
What you want is:
class Person
attr_accessor :name
#name = name
end
class People
#people
def initialize()
people = []
for i in 0..10
people[i] = Person.new
end
end
end
This creates another object that in turn contains 10 Person objects. This way there is no way for the same recursive problem to happen.
First of all, this is your Person class:
class Person
attr_accessor :name
def initialize(name)
#name = name
end
end
If you want another class to create x number of Person instances you can use the following PeopleCreator class:
class PeopleCreator
def self.create_person_for(names)
new.create(names)
end
def create(names)
names.map { |name| Person.new(name) }
end
end
I've used a class method in the PeopleCreator to be able to easily call the following:
names = %w(John Jane Jake)
PeopleCreator.create_person_for(names)
# => [#<Person:0x0000000a743150 #name="John">, #<Person:0x0000000a743128 #name="Jane">, #<Person:0x0000000a743100 #name="Jake">]
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I'm having the following error "Line 46: undefined local variable or method `app1' for main:Object (NameError)" when I run the following Ruby code about Methods and Classes on the compiler.Thanks in advance :D!!
class Apps
def initialize(name)
#name = name
end
def add_app
"#{name} has been added to the App Center.Approval is pending!!"
end
def app_approved
"#{name} has been approved by the App Center"
end
def app_posted
"Congratulations!!!!#{name} has been posted to the App Store."
end
end
class Fbapps
def initialize(name)
#name = name
#apps = []
end
def add_new(a_app)
#apps << a_app
"#{#app} has been added to the #{#apps} store!!"
end
def weekly_release
#apps.each do |app|
puts #app
end
#apps.each do |app|
app.add_app
app.app_approved
app.app_posted
end
end
end
apps = ["Bitstrip", "Candy Crush" , "Instapaper"]
apps = Fbapps.new("Apps")
apps.add_new(app1)
apps.add_new(app2)
apps.add_new(app3)
puts apps.weekly_release
app1 = Apps.new("Bitstrip")
app2 = Apps.new("Candy Crush")
app3 = Apps.new("Instapaper")
You need to create app1, app2, and app3 before adding them to apps:
apps = ["Bitstrip", "Candy Crush" , "Instapaper"]
app1 = Apps.new("Bitstrip")
app2 = Apps.new("Candy Crush")
app3 = Apps.new("Instapaper")
apps = Fbapps.new("Apps")
apps.add_new(app1)
apps.add_new(app2)
apps.add_new(app3)
puts apps.weekly_release
As noted there are other bugs in your classes, but they should be relatively trivial to fix given changing the order of execution as above.
Update: Here's your code updated to fix most of the bugs:
class Apps
attr_accessor :name
def initialize(name)
#name = name
end
def add_app
"#{name} has been added to the App Center.Approval is pending!!"
end
def app_approved
"#{name} has been approved by the App Center"
end
def app_posted
"Congratulations!!!! #{name} has been posted to the App Store."
end
end
class Fbapps
attr_accessor :name
def initialize(name)
#name = name
#apps = []
end
def add_new(a_app)
#apps << a_app
"#{a_app.name} has been added to the #{self.name} store!!"
end
def weekly_release
#apps.each do |app|
puts app.name
end
#apps.each do |app|
puts app.add_app
puts app.app_approved
puts app.app_posted
end
end
end
You're trying to do apps.add_new(app1) before you define app1. That line needs to go after app1 = Apps.new("Bitstrap") .
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i have simple, how to return array with class instances ? I'm trying to return the array, but this variable return an empty array.
For example :
class Library
def initialize
##books = []
end
def all
##books
end
def add_book(arg = {})
#book = Book.new(arg)
##books << #book
end
end
class Book
attr_accessor :name, :year, :author, :content
def initialize( arg = {})
#name = arg[:name]
#year = arg[:year]
#author = arg[:author]
#content = arg[:content]
end
end
##books is a Library class variable. I am using method add_book to put books into #books, but how can i return array of these instances ? Sorry for bad english.
Thanks in advance !
When you call the method new to create a new object, ruby runs the initialize method. Since the initialize method sets ##books to an empty array, of course Library.new.all will return an empty array.
Class variables are shared by all instances of a class, so it doesn't make sense to be resetting it when you initialize a new Library as you'd be zeroing out the books stored in all other Library instances. From your usage it looks like you want a plain instance variable:
class Library
def initialize
#books = []
end
# you could replace this method with a `attr_reader :books`
def all
#books
end
# consider changing the method signature to accept a Book instance
def add_book(arg = {})
#books << Book.new(arg)
end
end