Re: Scope of an @variable

Ruby
1

I’m also a newbie so others feel free to correct me as well :wink:

Your understanding is correct in that @name applies to the specific
instance of the class and the @@name applies to all instances of the
class.

Hope this example helps.

class Person
@@lastname = “Doe”
@name=""

def setLastName(newName)
	@@lastname =  newName
end

def changeName(newName)
	@name = newName
end

def sayName()
	"My name is " + @name
end

def fullName()
	"My full name is " + @name + " " + @@lastname
end

end

puts “—Defining John—\n”
p1 = Person.new()
p1.changeName(‘John’)
puts p1.sayName()
puts p1.fullName()

puts “\n”

puts “—Defining Jane—\n”
p2 = Person.new()
p2.changeName(‘Jane’)
puts p2.sayName()
puts p2.fullName()

puts “\n”

puts “—Changing Last Name—\n”
p1.setLastName(‘Smith’)

puts "John’s full name -> " + p1.fullName()
puts "Jane’s full name -> " + p2.fullName()

2

William (Bill) Froelich wrote:

I’m also a newbie so others feel free to correct me as well :wink:

Your understanding is correct in that @name applies to the specific
instance of the class and the @@name applies to all instances of the
class.

This may be wrong, but I like to think of @@ as a class variable and @
as a method variable. @@ is accessible by any method in the class and @
is accessible by the method only.

3

rtilley wrote:

This may be wrong, but I like to think of @@ as a class variable and @
as a method variable. @@ is accessible by any method in the class and @
is accessible by the method only.

You’re close. @ are instance variables. Any instance method in your
class can
access them.

(Maybe you’re thinking of local variables, which are defined within a
method and are accessible by that method only.)

Jeff

www.jeffcohenonline.com

4

Jeff C. wrote:

method and are accessible by that method only.)
Thanks Jeff! That makes sense. I was confusing @ vars with local vars.

5

On 15 Mar 2006, at 00:54, Jeff C. wrote:

rtilley wrote:

This may be wrong, but I like to think of @@ as a class variable
and @
as a method variable. @@ is accessible by any method in the class
and @
is accessible by the method only.

You’re close. @ are instance variables. Any instance method in your
class can
access them.

You can also access @ variables from a class method - ie
ClassName.function; @a_variable; end. They are local to each class
within a hierarchy, rather than @@ which would be shared among
classes in the hierarchy.

So:

class X
def X.var;
@var
end

def X.var=(v)
	@var=v
end

end

class Y<X;end

X.var=10
Y.var=20
X.var => 10
Y.var => 20

Cheers,
Benjohn

6

Hi –

On Fri, 17 Mar 2006, Benjohn B. wrote:

access them.
end
X.var => 10
Y.var => 20

Nice, isn’t it? It’s really just this:

obj = Object.new
def obj.var
@var
end

def obj.var=(v)
@var = v
end

with obj being a Class object. Plus the special-cased thing where the
subclasses get to call it (because the singleton class of X is
considered the superclass of the singleton class of Y).

You can also do:

class X
class << self # singleton class of X
attr_accessor :var
end
end

David

–
David A. Black ([email protected])
Ruby Power and Light, LLC (http://www.rubypowerandlight.com)

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