I have a class whose initialize method defines a few instance variables and does some calculations. I need to create about 60 objects of that class. Each object has an ID number at the end. E.g.:
object1 = Dynamic.new(x, y)
object2 = Dynamic.new(x, y)
object3 = Dynamic.new(x, y)
...
I could just define them all by hand, but that would be quite inefficient. Is there any way to dynamically create each object?
You can always make a loop and push all the objects into an array. An array position might also be needed for knowing which object is each. This isn't quite what you wanted (atleast I don't think so), but it should suffice.
class Dynamic
##instances_of_class = 0
def initialize(x,y)
#...
#array_position = ##instances_of_class
##instances_of_class += 1
end
end
ary = []
50.times do
ary << Dynamic.new(x,y)
end
Edit: This solution, as said in the comments, can cause bugs if you change the array, so here's an alternate solution.
require 'File.rb'
i = 1
varFile = File.open("File.rb","a+")
50.times do
varFile.puts "variable#{i} = Object.new"
i += 1
end
Inside of File.rb will be 50 uniquely named variables that you can use.
I would be curious to know why you need this. It's an unusual requirement, and often that means that you can avoid the problem instead of solving it. I think TheLuigi's solution would work, but if you use a class variable then these Id's will be shared across multiple classes. You can instead use an instance variable, with something like the following:
class A
def self.next_id
#id ||= 0 ; #id += 1
end
def initialize
#id = A.next_id
end
end
A.new
# => #<A:0x007fd6d414c640 #id=1>
A.new
# => #<A:0x007fd6d41454a8 #id=2>
If you just want sixty objects accessible from a variable, you should have them in an array referred to by a single variable.
objects = Array.new(60){Dynamic.new(x, y)}
Your object1, object2, ... will correspond to objects[0], objects[1], ... respectively.
Related
Ok i am not here to ask for an answer. But to be honest i am not really good in class variable. So i would appreciate you can guide me along with this piece of code.
I have read on class variable at those docs. I some what kind of understand it. But it comes to applying it for my own use. I would get confused.
class Square
##sqArray = {}
#attr_accessor :length
def initialize
if defined?(##length)
randno = "%s" % [rand(20)]
##length = randno.to_i
##sqArray = ##length
else
randno = "%s" % [rand(20)]
##length = randno.to_i
##sqArray = ##length
end
end
def Area
##area = ##length * ##length
return ##area
##sqArray[##length.to_sym] = ##area
puts ##sqArray
end
end
s1 = Square.new
puts s1.Area
Let me explain this piece of code. Basically every time i create a Square object it would go to initialize method. A random number will be generated and pass it to ##length, and ##length will be assigned to hash ##sqArray as it's key. But now the problem is when i create a new object s1. When i want to display the Area i want to test out to print the hash ##sqArray with it's length as it's key and area as it's value. But now the problem is only returning it's area only. e.g 114 only.
suppose to be e.g [ 24 => 114]
When defining the object's property (i.e. it's length), the correct approach is to use an instance variable, not a class variable. This is because (in your particular example), length is an attribute of a specific square and not something that applies to all squares. Your code should look something like this:
class Square
def initialize(length = rand(20))
#length = length
end
def area
#length * #length
end
end
s1 = Square.new
puts s1.area
Now, I am a little unclear what exactly you aim to achieve by use of that class variable ##sqArray - but for example, you could use this store a list of all defined Squares:
class Square
##squares_list = []
def self.all_known
##squares_list
end
def initialize(length = rand(20))
#length = length
##squares_list << self
end
def area
#length * #length
end
end
This would allow you to write code like:
s1 = Square.new #=> #<Square:0x0000000132dbc8 #length=9>
s2 = Square.new(20) #=> #<Square:0x000000012a1038 #length=20>
s1.area #=> 81
s2.area #=> 400
Square.all_known #=> [#<Square:0x0000000132dbc8 #length=9>, #<Square:0x000000012a1038 #length=20>]
Class variables have some odd behaviour and limited use cases however; I would generally advise that you avoid them when starting out learning Ruby. Have a read through a ruby style guide to see some common conventions regarding best practice - including variable/method naming (use snake_case not camelCase or PascalCase), whitespace, etc.
this is my first post and I'm quite new to programming/this site, so I apologise in advance if I'm doing something wrong/annoying.
I wanted to find a way to define objects without having to do so for each object. I came up with this
class Number
def initialize(name)
#name = name
end
def description
puts "I'm #{#name} "
end
end
a = ["zero", "one","two", "three", "four"]
for i in (0..5) do
a[i] = Number.new(a[i])
end
a[3].description
I'm hoping someone can tell me what kind of Frankensteins monster I've created?
It seems to work, a[3].description returns "I'm three" but does that mean three/a[3] exists as its own object and not an element of an array?
Furthermore if I try to do:
puts a[3]
I get:
<Context::Number:0x000000009b7fd0 #name="three">, #
To clarify I just want to know whether I have actually managed to create objects here, and why on earth when I try and access elements of my array I get that weird feedback (kind of seems like its accessing memory or something, but that is a little beyond me)
My thanks in advance for anyone who replies to this.
All objects stand on their own, regardless of whether they are contained by/in other objects such as Array instances.
Regarding this:
<Context::Number:0x000000009b7fd0 #name="three">, #
...did you mean you get that when you puts a[3] and not puts a?
Every instance of Object and its subclasses has a to_s method that returns a string representation of the object. Since you did not override that in your Number class, it used the default implementation defined in class Object. It is showing you:
1) the class name (I presume you defined Number in side a class or module named Context)
2) the object id (a unique id in the Ruby runtime)
3) the string representation of its instance variable(s)
Also, regarding this:
a = ["zero", "one","two", "three", "four"]
This is equivalent and easier to type (I use 2 spaces for better readability):
%w(zero one two three four)
Also, as Ilya pointed out, map will simplify your code. I'll go a little further and recommend this to do the array initialization:
a = %w(zero one two three four).map { |s| Number.new(s) }
Yes, you have created objects. It's just how Ruby represents a class as a string.
class MyClass
attr_accessor :one, :two
def initialize(one, two)
#one, #two = one, two
end
end
my_class = MyClass.new(1, 2)
my_class.to_s # #<MyClass:0x007fcacb8c7c68>
my_class.inspect # #<MyClass:0x007fcacb8c7c68 #one=1, #two=2>
I'm getting familiar with ruby send method, but for some reason, I can't do something like this
a = 4
a.send(:+=, 1)
For some reason this doesn't work. Then I tried something like
a.send(:=, a.send(:+, 1))
But this doesn't work too. What is the proper way to fire plus equals through 'send'?
I think the basic option is only:
a = a.send(:+, 1)
That is because send is for messages to objects. Assignment modifies a variable, not an object.
It is possible to assign direct to variables with some meta-programming, but the code is convoluted, so far the best I can find is:
a = 1
var_name = :a
eval "#{var_name} = #{var_name}.send(:+, 1)"
puts a # 2
Or using instance variables:
#a = 2
var_name = :#a
instance_variable_set( var_name, instance_variable_get( var_name ).send(:+, 1) )
puts #a # 3
See the below :
p 4.respond_to?(:"+=") # false
p 4.respond_to?(:"=") # false
p 4.respond_to?(:"+") # true
a+=1 is syntactic sugar of a = a+1. But there is no direct method +=. = is an assignment operator,not the method as well. On the other hand Object#send takes method name as its argument. Thus your code will not work,the way you are looking for.
It is because Ruby doesn't have = method. In Ruby = don't work like in C/C++ but it rather assign new object reference to variable, not assign new value to variable.
You can't call a method on a, because a is not an object, it's a variable, and variables aren't objects in Ruby. You are calling a method on 4, but 4 is not the thing you want to modify, a is. It's just not possible.
Note: it is certainly possible to define a method named = or += and call it, but of course those methods will only exist on objects, not variables.
class Fixnum
define_method(:'+=') do |n| self + n end
end
a = 4
a.send(:'+=', 1)
# => 5
a
# => 4
This might miss the mark a bit, but I was trying to do this where a is actually a method dynamically called on an object. For example, with attributes like added_count and updated_count for Importer I wrote the following
class Importer
attr_accessor :added_count, :updated_count
def increment(method)
send("#{method}=", (send(method) + 1))
end
end
So I could use importer.increment(:added_count) or importer.increment(:updated_count)
Now this may seem silly if you only have these 2 different counters but in some cases we have a half dozen or more counters and different conditions on which attr to increment so it can be handy.
Two problems, that probably are related:
I'm retreiving a number of 'persons' from a YAML-file to an array, and now i'm trying to create classes from that array.
These objects are then to placed in a new array.
It actually works out fine, if you dont consider the fact that the object added last replaces all the previously added.
In my case i get five identical copies of object #5, where i rather like to see five different ones.
My guess is that the error results somewhere in my iterator to get all the 'persons' from the YAML.
I'm getting a cuople of warnings, regarding the 're-use' of constants:
NEWSTR and NEWAL.
getPost = 0
loopa = 0
while loopa < personsInYAML
NEWSTR = TEST.fetch(getPost)
NEWAL = NEWSTR.split(' ')
getPost+=1
puts "*****************************************"
nyloop = loopa+1
puts "PERSON: " + nyloop.to_s + " name: " + NEWAL.fetch(1)
nameToArray = Person.new
outputArray.insert(loopa, nameToArray)
loopa+=1
end
Persons-class
class Person
def initialize
#name
#age
#length
#weight
#misc
end
def name
name = NEWAL.fetch(1)
return name
end
if NEWAL.include?("age:")
def age
x = NEWAL.index("age:")+1
age = NEWAL.fetch(x)
return age
end
end
if NEWAL.include?("length:")
def length
x = NEWAL.index("length:")+1
length = NEWAL.fetch(x)
return length
end
end
if NEWAL.include?("weight:")
def weight
x = NEWAL.index("weight:")+1
weight = NEWAL.fetch(x)
return weight
end
end
if NEWAL.include?("misc:")
def misc
x = NEWAL.index("misc:")+1
misc = NEWAL.fetch(x)
return misc
end
end
end
You're taking the wrong approach to populating your Person class. The only thing your loop is doing is to create brand new Person classes and stick them in an array. It isn't actually initializing the person class at all.
It looks like what you are trying to do is to use a constant (which you don't hold constant) to pass information to the Person class. However, the code that you have in your Person class that is outside of the methods is only going to be run once - when the class loads for the first time, NOT at the time that you make a new Person.
You'd be better off changing your initialize method to take some arguments, and to create the class with appropriate arguments within the loop.
def initialize(name, age = nil, length = nil, weight = nil, misc = nil)
# assign instance variables here
#name = name
...
end
You appear to be trying to create dynamic accessors to the instance variables. This doesn't make a whole lot of sense. Just define accessors on all of them, and handle the case where the instance variables are nil in whatever code is calling the Person class.
I have the following two variables:
a = 1;
b = 'a';
I want to be able to do
SOMETYPEOFEVALUATION(b) = 2;
so that the value of variable a is now set to 2.
a # => 2
Is this possible?
Specifically, I am working with the Facebook API. Each object has a variety of different connections (friends, likes, movies, etc). I have a parser class that stores the state of the last call to the Facebook API for all of these connections. These states are all named corresponding to the the GET you have to call in order to update them.
For example, to update the Music connection, you use https://graph.facebook.com/me/music?access_token=... I store the result in a variable called updated_music. For books, its updated_books. If I created a list of all these connection type names, I ideally want to do something like this.
def update_all
connection_list.each do |connection_name|
updated_SomeTypeOfEvalAndConcatenation(connection_name) = CallToAPI("https://graph.facebook.com/me/#{connection_name}?access_token=...")
end
end
Very new to both Rails and StackOverflow so please let me know if there is a better way to follow any conventions.
Tried the below.
class FacebookParser
attr_accessor :last_albums_json,
def update_parser_vars(service)
handler = FacebookAPIHandler.new
connections_type_list = ['albums']
connections_type_list.each do |connection_name|
eval "self.last_#{connection_name}_json = handler.access_api_by_content_type(service, #{connection_name})['data']"
end
#self.last_albums_json = handler.access_api_by_content_type(service, 'albums')['data']
end
end
And I get this error
undefined local variable or method `albums' for #<FacebookParser:0xaa7d12c>
Works fine when I use line that is commented out.
Changing an unrelated variable like that is a bit of a code smell; Most programmers don't like it when a variable magically changes value, at least not without being inside an enclosing class.
In that simple example, it's much more common to say:
a=something(b)
Or if a is a more complex thing, make it a class:
class Foo
attr_accessor :a
def initialize(value)
#a = value
end
def transform(value)
#a = "new value: #{value}"
end
end
baz = "something"
bar = Foo.new(2)
bar.a
=> 2
bar.transform(baz)
bar.a
=> "new value: something"
So while the second example changes an internal variable but not through the accessor, at least it is part of an encapsulated object with a limited API.
Update Ah, I think the question is how do do like php's variable variables. As mu suggests, if you want to do this, you are probably doing the wrong thing... it's a concept that should never have been thought of. Use classes or hashes or something.
how about
eval "#{b}=2"
and with instance variables you can also do instance_variable_set("#name", value)
EDIT:
you can also use send method if you have a setter defined(and you have), try this:
class FacebookParser
attr_accessor :last_albums_json,
def update_parser_vars(service)
handler = FacebookAPIHandler.new
connections_type_list = ['albums']
connections_type_list.each do |connection_name|
send("last_#{connection_name}_json=",
handler.access_api_by_content_type(
service, connection_name)['data']))
end
end
end
problem with your original code is that
eval ".... handler.access_api_by_content_type(service, #{connection_name})"
would execute
... handler.access_api_by_content_type(service, albums)
# instead of
... handler.access_api_by_content_type(service, 'albums')
so you had to write
eval ".... handler.access_api_by_content_type(service, '#{connection_name}')" <- the quotes!
this is why people usually avoid using eval - it's easy to do this kind of mistakes
These sort of things are not usually done using local variables and their names in Ruby. A usual approach could include hashes and symbols:
data = Hash.new
data[:a] = 1 # a = 1
b = :a # b = 'a'
and then, later
data[b] = 2 # SOMETYPEOFEVALUATION(b) = 2
data[:a] # => 2