# Ruby's a = b vs PHP5's $obj1 =& $obj2 **URL:** \ **Category:** Ruby\ **Created:** [September 27, 2007, 3:45pm UTC](https://www.ruby-forum.com/t/rubys-a-b-vs-php5s-obj1-obj2/115676 "2007-09-27T15:45:08Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![winterheat](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7993a0/32.png) [@winterheat](https://www.ruby-forum.com/u/winterheat)\ **Post date:** [September 27, 2007, 3:45pm UTC](https://www.ruby-forum.com/t/rubys-a-b-vs-php5s-obj1-obj2/115676/1 "2007-09-27T15:45:08Z")
Just want to confirm Ruby’s a = b is the same as PHP5’s $obj1 = $obj2 in other words, the reference is copied. While $obj1 =& $obj2 or $obj1 = &$obj2 in both PHP4 and PHP5 isn’t the same as Ruby’s a = b $obj1 and $obj2 just become synonyms… and after $obj1 = new Foo(“foo1”); $obj2 =& $obj1 $obj2 = new Foo(“bar1”); $obj1 and $obj2 have the same content, as they are just synonyms. (not a clone, not same reference, but just synonyms). The “foo1” object is garbage-collected since no one is referencing it. this is giving me an initial headache… until maybe after i get used to it. ---
**Author:** ![winterheat](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7993a0/32.png) [@winterheat](https://www.ruby-forum.com/u/winterheat)\ **Post date:** [September 27, 2007, 3:54pm UTC](https://www.ruby-forum.com/t/rubys-a-b-vs-php5s-obj1-obj2/115676/2 "2007-09-27T15:54:00Z")
On 9/27/07, SpringFlowers AutumnMoon [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > $obj1 and $obj2 just become synonyms… > > ## this is giving me an initial headache… until maybe after i get used to it. > > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). IMO it’s giving you a headache because you’re trying to compare a clean, well thought out language like Ruby to a hacked-together-over-many-years language like PHP. Ruby acts exactly as you would expect it to. a = Object.new # =\> a now points to this object a = b # =\> a and b now point to the same object b = Object.new # =\> b now points to a new object, a still points to the original object. The faster you stop comparing to PHP and start thinking in terms of how languages are supposed to work, the better. Jason ---
**Author:** ![winterheat](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7993a0/32.png) [@winterheat](https://www.ruby-forum.com/u/winterheat)\ **Post date:** [September 27, 2007, 3:55pm UTC](https://www.ruby-forum.com/t/rubys-a-b-vs-php5s-obj1-obj2/115676/3 "2007-09-27T15:55:46Z")
On 9/27/07, SpringFlowers AutumnMoon [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > While > > this is giving me an initial headache… until maybe after i get used to > it. in ruby: a = Hash.new # a is a reference to Hash object #1 b = a # both a and b point to the same object a[1] = ‘a’ # and b[1] is ‘a’ as well but b = Hash.new # now a points to Hash obj #1 and b to #2 b[1] = ‘c’ # a[1] is still ‘a’ i.e. assignment may destroy the link. ---
**Author:** ![winterheat](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7993a0/32.png) [@winterheat](https://www.ruby-forum.com/u/winterheat)\ **Post date:** [September 27, 2007, 8:08pm UTC](https://www.ruby-forum.com/t/rubys-a-b-vs-php5s-obj1-obj2/115676/4 "2007-09-27T20:08:14Z")
Quoth SpringFlowers AutumnMoon: > While > > this is giving me an initial headache… until maybe after i get used to > it. PHP’s $var1 =& $var2 seems to be setting a reference to a reference. I think ruby is more like PHP’s $var1 = $var2, though I could be wrong. HTH, ---
**Author:** ![winterheat](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7993a0/32.png) [@winterheat](https://www.ruby-forum.com/u/winterheat)\ **Post date:** [September 27, 2007, 4:35pm UTC](https://www.ruby-forum.com/t/rubys-a-b-vs-php5s-obj1-obj2/115676/5 "2007-09-27T16:35:04Z")
SpringFlowers AutumnMoon wrote: > While > > this is giving me an initial headache… until maybe after i get used to > it. Hello, In PHP, $obj1 = & $obj2 means that both $obj1 and $obj2 points to the same content. Its like hardlinks in Unix. In Ruby, depends of type of variable. If type of variable as object, its work like as PHP. If type of variable as a number, its not work as PHP. See an example: sysdebug(main):014:0\> class A sysdebug(main):015:1\> def setName(name) sysdebug(main):016:2\> @name = name sysdebug(main):017:2\> end sysdebug(main):018:1\> def putsName sysdebug(main):019:2\> puts @name sysdebug(main):020:2\> end sysdebug(main):021:1\> end =\> nil sysdebug(main):022:0\> sysdebug(main):023:0\* sysdebug(main):024:0\* a = A.new A =\> #\ sysdebug(main):025:0\> b = a =\> #\ sysdebug(main):026:0\> a.setName(‘Jonas’) =\> “Jonas” sysdebug(main):027:0\> a.putsName Jonas =\> nil sysdebug(main):028:0\> b.putsName Jonas =\> nil sysdebug(main):029:0\> b.setName(‘Ana’) =\> “Ana” sysdebug(main):030:0\> a.putsName Ana =\> nil But in number types: sysdebug(main):031:0\> num1 = 1 =\> 1 sysdebug(main):032:0\> num2 = num1 =\> 1 sysdebug(main):033:0\> num2 =\> 1 sysdebug(main):034:0\> num1 = 2 =\> 2 sysdebug(main):035:0\> num2 =\> 1 sysdebug(main):036:0\> Regards, ---
**Author:** ![winterheat](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7993a0/32.png) [@winterheat](https://www.ruby-forum.com/u/winterheat)\ **Post date:** [September 27, 2007, 9:02pm UTC](https://www.ruby-forum.com/t/rubys-a-b-vs-php5s-obj1-obj2/115676/6 "2007-09-27T21:02:19Z")
On Sep 27, 2007, at 10:34 AM, Jonas Roberto de Goes Filho (sysdebug) wrote: > PHP, $obj1 = & $obj2 means that both $obj1 and $obj2 points to the > same content. Its like hardlinks in Unix. > > In Ruby, depends of type of variable. If type of variable as > object, its work like as PHP. If type of variable as a number, its > not work as PHP. There is no need to think of ‘numbers’ as a special case in Ruby. And I don’t think your example even illustrates that they are different. > =\> 2 > sysdebug(main):035:0\> num2 # num2 still references the > object ‘1’ > =\> 1 > sysdebug(main):036:0\> The trick is to think of integer literals not as values but as references to objects. 1 is not the “value” 1 but is a reference to the Fixnum object that behaves like the number 1 and there is only a single Fixnum object that behaves that way (i.e. Fixnum objects are _not_ containers for integer values). Note: Not everyone thinks of Ruby integer’s in this way but IMHO it makes Ruby’s assignment semantics very simple and regular. Gary W. ---
**Author:** ![winterheat](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7993a0/32.png) [@winterheat](https://www.ruby-forum.com/u/winterheat)\ **Post date:** [September 27, 2007, 9:44pm UTC](https://www.ruby-forum.com/t/rubys-a-b-vs-php5s-obj1-obj2/115676/7 "2007-09-27T21:44:16Z")
> In PHP, $obj1 = & $obj2 means that both $obj1 and $obj2 points to the > same content. Its like hardlinks in Unix. That is from C++. Those are “reference” semantics. It causes two names to refer to the same spot in memory where a value is stored. Either name can be used to change the value at that spot in memory, and since both names always refer to that same spot in memory, either name can be used to retrieve the new value there. > In Ruby, depends of type of variable. If type of variable as object, its > work like as PHP. If type of variable as a number, its not work as PHP. > > See an example: > > sysdebug(main):014:0\> class A > sysdebug(main):015:1\> def setName(name) > sysdebug(main):016:2\> @name = name > sysdebug(main):017:2\> end > sysdebug(main):018:1\> def putsName > sysdebug(main):019:2\> puts @name > sysdebug(main):020:2\> end > sysdebug(main):021:1\> end > =\> nil > sysdebug(main):022:0\> > sysdebug(main):023:0\* > sysdebug(main):024:0\* a = A.new > A > =\> #\ > sysdebug(main):025:0\> b = a > =\> #\ > sysdebug(main):026:0\> a.setName(‘Jonas’) > =\> “Jonas” > sysdebug(main):027:0\> a.putsName > Jonas > =\> nil > sysdebug(main):028:0\> b.putsName > Jonas > =\> nil > sysdebug(main):029:0\> b.setName(‘Ana’) > =\> “Ana” > sysdebug(main):030:0\> a.putsName > Ana > =\> nil > > But in number types: > > sysdebug(main):031:0\> num1 = 1 > =\> 1 > sysdebug(main):032:0\> num2 = num1 > =\> 1 > sysdebug(main):033:0\> num2 > =\> 1 The difference is this next step: > sysdebug(main):034:0\> num1 = 2 > =\> 2 > sysdebug(main):035:0\> num2 > =\> 1 > sysdebug(main):036:0\> You used assignment in that step. In other words, you reassigned to num1. In your previous example you never used assignment to reassign anything to a; instead you changed the object that a referred to. ---
**Author:** ![winterheat](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7993a0/32.png) [@winterheat](https://www.ruby-forum.com/u/winterheat)\ **Post date:** [September 27, 2007, 9:27pm UTC](https://www.ruby-forum.com/t/rubys-a-b-vs-php5s-obj1-obj2/115676/8 "2007-09-27T21:27:35Z")
Jonas Roberto de Goes Filho (sysdebug) wrote: > In PHP, $obj1 = & $obj2 means that both $obj1 and $obj2 points to the > same content. Its like hardlinks in Unix. > > In Ruby, depends of type of variable. If type of variable as object, its > work like as PHP. If type of variable as a number, its not work as PHP. The first pargraph may or may not be correct. I do not know, since I know nothing about PHP and little about UNIX. > In Ruby, depends of type of variable. If type of variable as object, > its > work like as PHP. If type of variable as a number, its not work as > PHP. The second cannot be correct. Variables in Ruby do not have a type, they reference objects. Moreover, when b is a variable a = b always means the same thing, and that does not depend on the type of object referenced by b! The line (a = b) means that the variables, a and b, reference the same object UNTIL either reference is changed. Changing the reference to one will mean they no longer refer to the same object. Changing some reference within the object will not change what either variable refers to, BUT the common object referred to is modified. This is true for all types of objects in Ruby. In Jonas’ example, the difference is that the object created by a = A.new is capable of having a name and the line a.setName(‘Jonas’) creates a reference to a string within that object. Since a and b still refer to the same object either one can change the reference, @name, i.e. they can change the name and then both a and b will know about that change. Once either a or b refers to a different object the link or common reference for a and b is broken! The Fixnum class is different from the A class in that the only way to change the value of a Fixnum object is to create a new object and hence a new reference; while in A changing the name does not create a new object, it modifies the object already created. I think the basic problem is that in many languages variables refer to a particular place in memory with a given structure. Ruby on the other hand makes a variable refer to an object not a place in memory. Anyone coming from the first type of language to Ruby has a big adjustment to make in handling the language. (I know I did when I first looked at Python.) Often it doesn’t seem to matter, but that just makes the adjustment harder because the difference is less visible. Ian W.