# Objects put into a declared array **URL:** \ **Category:** Ruby\ **Created:** [February 24, 2009, 12:15pm UTC](https://www.ruby-forum.com/t/objects-put-into-a-declared-array/161216 "2009-02-24T12:15:47Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![paradise](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/8e7dd6/32.png) [@paradise](https://www.ruby-forum.com/u/paradise)\ **Post date:** [February 24, 2009, 12:15pm UTC](https://www.ruby-forum.com/t/objects-put-into-a-declared-array/161216/1 "2009-02-24T12:15:47Z")
Hi I’ve got this misunderstanding of how to use arrays and objects stored there in (note I’m actually using Shoes if this has any bearing on my problem). below is a bit of code i’ve written that creates an array of 25 places. @myarray = Array(1…25) I then want to “install” a bona fide object like a shape into each 25 places. so i do this… 1.upto @myarray.length do |p| @myarray[p] = oval(0,0,20,20) @myarray[p].move = x,y note: x & y being defined else where so each shape is visable on screen or can it be @myarray[p] = oval(0,0,20,20).move x,y? if i use a local variable when defining ashape and do this @myarray[p] \<\< ashape then it works without the error that i get presntly which is move is private and refers to the actual line @array[p].move = x,y any explanations would be great and thoughts on best practices with this sort of thing would be grateful. dave. ---
**Author:** ![paradise](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/8e7dd6/32.png) [@paradise](https://www.ruby-forum.com/u/paradise)\ **Post date:** [February 24, 2009, 1:08pm UTC](https://www.ruby-forum.com/t/objects-put-into-a-declared-array/161216/2 "2009-02-24T13:08:52Z")
Dave L. wrote: > Hi I’ve got this misunderstanding of how to use arrays and objects > stored there in (note I’m actually using Shoes if this has any bearing > on my problem). > > below is a bit of code i’ve written that creates an array of 25 places. > @myarray = Array(1…25) This is not necessary, the array will grow as you add things to it. Given the code you have shown, you can just as well do: @myarray = [] > I then want to “install” a bona fide object like a shape into each 25 > places. > so i do this… > 1.upto @myarray.length do |p| Remember, Ruby arrays are 0-based, so you array of 25 items is indexed 0 to 24. Using ‘p’ as a variable name is not recommended, because ‘p’ is also a built-in method. Also, a more common way to do this (and noticing the array is now empty if defined as above) would be (0…25).each do |p| > ``` > @myarray[p] = oval(0,0,20,20) > @myarray[p].move = x,y > > ``` I think you mean to do @myarray[p].move x, y > note: x & y being defined else where so each shape is visable on screen > > or can it be @myarray[p] = oval(0,0,20,20).move x,y? This would work, too, though you may need to do @myarray[p] = oval(0,0,20,20).move(x,y) -Justin ---
**Author:** ![paradise](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/8e7dd6/32.png) [@paradise](https://www.ruby-forum.com/u/paradise)\ **Post date:** [February 24, 2009, 2:29pm UTC](https://www.ruby-forum.com/t/objects-put-into-a-declared-array/161216/3 "2009-02-24T14:29:00Z")
Hello dave, On Tue, Feb 24, 2009 at 4:45 PM, Dave L. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > below is a bit of code i’ve written that creates an array of 25 places. > @myarray = Array(1…25) While that will indeed create an array of length 25, it does a bit more: $: irb 01\> Array(1…4) → [1, 2, 3, 4] As you can see it also populates the array with each value in the range 1…4. The way the Array method works is to convert its argument (in this case, the Range 1…4) into an array [1]. The simpler way to create an array with 4 ‘slots’ is: 02\> Array.new(4) → [nil, nil, nil, nil] Here’s a third way that populates the array with a given object, instead of nil. 03\> Array.new(4, ‘four’) → [“four”, “four”, “four”, “four”] And this way allows you to fill the array one item at a time by yielding to your block. 04\> Array.new(4) {|i| i \* i } → [0, 1, 4, 9] > I then want to “install” a bona fide object like a shape into each 25 > places. > so i do this… > 1.upto @myarray.length do |p| > @myarray[p] = oval(0,0,20,20) It’s best if you can create populated arrays instead of creating then populating them in two steps. The third form i mentioned above will handle most cases. Once you have an array, there are many idiomatic ways to traverse it: $ irb # edited 01\> array = [0, 1, 2] 02\> array.each {|item| puts item } That’s of course the most straightforward. The following creates another array with each item transformed or ‘mapped’ by the provided block: 03\> array.map {|x| x \* x } → [0, 1, 4] That’s pretty close to what your code above was doing except that it results in second array. To perform the transformation in place, use #map! [2]. Here’s another fun one that i’ll let you explore yourself: 04\> array.inject(0) {|sum, x| sum += x } → 3 There are many more, check out the doco on Array and Enumerable. > or can it be @myarray[p] = oval(0,0,20,20).move x,y? Not generally. The whole right-hand-side is evaluated before assignment, so that line would assign the result of the #move method to @my\_array[p]. It’s possible the #move method returns the object on which it was invoked (self), in which case this would work, but that’s a special case. > if i use a local variable when defining ashape and do this > @myarray[p] \<\< ashape > > then it works without the error that i get presntly which is > > move is private and refers to the actual line @array[p].move = x,y I don’t know Shoes, but i’d bet you want that to be @array[p].move(x, y) The way you’ve got it ruby will look for an attribute writer method[3], #move=, on that object and try to assign the array [x, y] to it. It would be odd to have an attribute named move (since it’s a verb) - doesn’t sound like something \_why would create :). > any explanations would be great and thoughts on best practices with this > sort of thing would be grateful. > > dave. Hope some of that helps. Cheers, lasitha. References: [1] [module Kernel - RDoc Documentation](http://ruby-doc.org/core-1.9/classes/Kernel.html#M006081) [2] [http://ruby-doc.org/core-1.9/classes/Array.src/M002048.html](http://ruby-doc.org/core-1.9/classes/Array.src/M002048.html) [3] [http://www.ruby-doc.org/docs/ProgrammingRuby/html/tut\_classes.html#S2](http://www.ruby-doc.org/docs/ProgrammingRuby/html/tut_classes.html#S2) ---
**Author:** ![paradise](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/8e7dd6/32.png) [@paradise](https://www.ruby-forum.com/u/paradise)\ **Post date:** [February 25, 2009, 10:36am UTC](https://www.ruby-forum.com/t/objects-put-into-a-declared-array/161216/4 "2009-02-25T10:36:46Z")
Justin & lasitha, Many thanks for replying, Muchly appreciated. My aim was to have an array of shapes that can be controlled my the array. I think both this and the other below are what i was after and so hopefully i can continue my little shoes program. > (0…25).each do |p| > ``` > @myarray[p] = oval(0,0,20,20) > @myarray[p].move = x,y > > ``` > ``` > @myarray[p] = oval(0,0,20,20).move(x,y) > > ``` > The way you’ve got it ruby will look for an attribute writer > method[3], #move=, on that object and try to assign the array [x, y] > to it. It would be odd to have an attribute named move (since it’s a > verb) - doesn’t sound like something \_why would create :). I firmly believed it was my misunderstanding of what i had read that caused me the problem regarding the above. I saw the way it was used by Karel Minařík but I’m a bit pig headed (stubborn) and wanted to inject something of me into my code. Hope this helps someone else with a similar problem. and I will goto those links and read up some more. thanks again, dave.