Why does this return nil for @city?
class Url
def initialize(city,quary,catagory,minask,maxask)
@city = city
@quary = quary
@cat = catagory
@min = minask
@max = maxask
end
puts @city
end
a = Url.new(‘spokane’,“tires”,“pts”,“0”,“1000”)
a
2010/8/28 Cameron V. [email protected]:
Why does this return nil for @city?
Because when you use @city outside a method definition, it is an
instance variable of you class Url [1] and not of an instance of you
class.
add
def city
puts @city
end
and call a.city to get what you want.
Cheers,
JJ Fleck
[1] I’m not 100% sure of the naming but what is sure is that the @city
you use is not an instance method of your instance a.
I get what your saying,
But the problem I’m having is I want to build a URL string from the
intit parameters… I need to concantinate them and add some other
stuff…
So I guess I just pass them to the class and use them as parameters?..
no need to init them as instance variables?.. alright…
thanks for the reply I will mess with it.
On 28.08.2010 18:17, Cameron V. wrote:
puts @city
end
a = Url.new(‘spokane’,“tires”,“pts”,“0”,“1000”)
a
Others have identified the basic issue (your puts statement accesses a
member of the class and not of the instance) but I’d like to add a few
other remarks. First, the name Url might cause confusion because
someone might think it is a generic URL handling class (like class URI
for example).
What you basically should do is add attribute accessors for your
instance variables, e.g.
class Url
attr :city
end
Then you can do
a = Url.new …
puts a.city
But: you can make your life much simpler by resorting to Struct:
CityUrl = Struct.new :city, :quary, :catagory, :minask, :maxask
This gives you a proper initialize, attribute accessors and a few more
things for free.
irb(main):008:0> a = CityUrl.new(‘spokane’,“tires”,“pts”,“0”,“1000”)
=> #<struct CityUrl city=“spokane”, quary=“tires”, catagory=“pts”,
minask=“0”, maxask=“1000”>
irb(main):009:0> a.city
=> “spokane”
Btw, from the naming and values of “minask” and “maxask” it seems these
should be rather used with integer values. Even if you read them as
strings from some sort of file your application logic will become much
easier if you convert those strings on reading into ints and then go
from there. Otherwise you will have to convert them all the time you
want to use them which is inefficient, error prone (you might forget a
location) and tedious to change if you need to at one point. Also, you
depend on the format of the single source which might make it difficult
to pull the data from other sources later. Basically it’s best to
always do something like
external representation -> import (load) converts into internal
representation -> work with that internal representation throughout the
application -> export (store) converts to external representation
Kind regards
robert
On Sat, Aug 28, 2010 at 11:17 AM, Cameron V.
[email protected]wrote:
puts @city
end
a = Url.new(‘spokane’,“tires”,“pts”,“0”,“1000”)
aPosted via http://www.ruby-forum.com/.
This is basically what Jean said, but I figured it might be easier to
follow
if you can actually see it.
class Url
self is the class Url
puts “outside initialize 1, self is #{self.inspect}”
def initialize(city,quary,catagory,minask,maxask)
@city = city
@quary = quary
@cat = catagory
@min = minask
@max = maxask
# self is an instance of Url
puts “Inside initialize 3, self is #{self.inspect}”
end
self is the class Url
puts “outside initialize 2, self is #{self.inspect}”
def render
# self is an instance of Url
puts “Inside initialize 4, self is #{self.inspect}”
@city + @quary + @cat + @min + @max
end
end
a = Url.new(‘spokane’,“tires”,“pts”,“0”,“1000”)
result = a.render
puts “result is #{result.inspect}”