Arrays(setters and getters)

Ruby
1

whats wrong with that

class Whatever
attr_accessor :array
@array
def initialize
@array = []
@array = [“apple”, “banana”, “peach”]
end
def array []= (i,value) # setter
@array[i] = value
end
def array[] (i) #getter
@array[i]
end
end

shehio = Whatever.new
puts shehio.inspect
puts shehio.array
puts shehio.array[0]
puts shehio.array[1]
puts shehio.array[2]
shehio.array[0] = 1
shehio.array[0] = 2
shehio.array[0] = 3
puts shehio.array[0]
puts shehio.array[1]
puts shehio.array[2]

2

On Sat, Sep 3, 2011 at 6:16 PM, jack jones [email protected]
wrote:

end
puts shehio.array[2]
shehio.array[0] = 1
shehio.array[0] = 2
shehio.array[0] = 3
puts shehio.array[0]
puts shehio.array[1]
puts shehio.array[2]

–
Posted via http://www.ruby-forum. http://www.ruby-forum.com/

whatever.array returns the array object, then whatever.array.[]=(1,2) is
invoked on the array object, you can’t define that from your whatever
class
unless you define it on the array itself, in the initialize method or
something.

Not to worry, though, array already implements that interface and it
does
what you’re trying to define. Just do this:

class Whatever
attr_accessor :array
def initialize
@array = [“apple”, “banana”, “peach”]
end
end

3

Isn’t there any other way to invoke shehio.array[index] = sth … Can
this be achieved?

4

hi Shehio,

so, a couple of things…

whats wrong with that

class Whatever
attr_accessor :array
@array ### THIS IS NOT NECESSARY
def initialize
@array = [] ### THIS IS NOT NECESSARY EITHER
@array = [“apple”, “banana”, “peach”]
end
### THE FOLLOWING IS NOT NECESSARY
def array []= (i,value) # setter
@array[i] = value
end
def array[] (i) #getter
@array[i]
end
end

this code could read:

class Whatever

  attr_accessor :array

  def initialize
    @array = ["apple", "banana", "peach"]
  end

end

and all of this will work just fine:

shehio = Whatever.new
puts shehio.inspect
puts shehio.array
puts shehio.array[0]
puts shehio.array[1]
puts shehio.array[2]
shehio.array[0] = 1
shehio.array[0] = 2
shehio.array[0] = 3
puts shehio.array[0]
puts shehio.array[1]
puts shehio.array[2]

  • j
5

On Sat, Sep 3, 2011 at 6:31 PM, jack jones [email protected]
wrote:

Isn’t there any other way to invoke shehio.array[index] = sth … Can
this be achieved?

–
Posted via http://www.ruby-forum.com/.

Yes, but not from instances of Whatever. You can fake out the object you
return from the array method

class Whatever

this class does nothing that real arrays don’t already do, so…

class FakeArray
def initialize
@real_array = [“apple”, “banana”, “peach”]
end
def []=(index, val)
@real_array[index] = val
end
def
@real_array
end
end

attr_accessor :array
def initialize
@array = FakeArray.new
end

end

What are you trying to do that you think you need this capability?

6

When you write this:

class Dog
@x
end

you create what’s called a ‘class instance variable’, and you access it
using the class like this:

Dog.x = 10 #setter
puts Dog.x #getter

However, just like with regular instance variables, you have to define
accessor methods in order to access a ‘class instance
variable’:

class Dog

@dog

def Dog.x=(val)
@x = val
end

def Dog.x
@x
end

end

Dog.x = 10
puts Dog.x

–output:–
10

@ variables attach themselves to whatever self is at the moment. Inside
a class, but outside any defs, self is equal to the class. Inside a
def, self is equal to the object that called the method. If that
doesn’t make any sense, don’t worry about it.