On Tue, Feb 8, 2011 at 12:06 PM, Phil Crissman <[email protected]>wrote:
> > Phil > > > On Tue, Feb 8, 2011 at 11:26 AM, David Kahn > <[email protected]>wrote: > >> >> >> On Tue, Feb 8, 2011 at 10:34 AM, Frederick Cheung < >> [email protected]> wrote: >> >>> On Feb 8, 3:33 pm, David Kahn <[email protected]> wrote: >>> > On Tue, Feb 8, 2011 at 9:06 AM, Frederick Cheung < >>> [email protected] >>> > >>> > I see, I guess I got confused as I use ActiveRecord so much and within >>> a >>> > each block, by setting values and calling save it of course saves the >>> > object. Is there a way to achieve what I am presenting, though, passing >>> a >>> > batch of variables and having them operated on and changed? >>> >>> that is very different. doing some_object.foo = 'bar' is calling a >>> method on an object that changes its state, whereas >>> foo = bar just points a local variable at something new. (and in >>> addition Fixnums/BigDecimal are immutable - there is no method you can >>> call on a number to change it into another nmber) >>> >> >> I think I am starting to see, maybe. Hopefully not being too annoying >> here. >> >> It seems rather strange to me that if you have an object, i.e. a string >> that it should behave differently than my Account object.... the string#=() >> method is still a property, right? -- no different really than >> account#name=(), so seems it would be logical that if I can do >> account.name = 'x' within an iterator, that doing string='y' should also >> work, but as we see it does not (lets put the Fixnums and BigDecimal aside >> as I understand as a property they are re-created rather than modified). >> >> arr.each {|account| account.name = 'x'} >> >> arr.each {|string| string=('y')} >> >> .... they seem to me to be the same thing, unless objects are really not >> the same. >> >> >> But with another experiment I see something interesting --- if I >> instantiate a string formally as an object, then I do get the by reference >> relationship in an array: >> >> ruby-1.9.2-p136 :098 > str = String.new('David') >> => "David" >> ruby-1.9.2-p136 :099 > arr = [str] >> => ["David"] >> ruby-1.9.2-p136 :100 > arr.each {|s| str = 'new val'} >> => ["David"] >> ruby-1.9.2-p136 :101 > str >> => "new val" >> >> But if I just do it as a normal assignment, I do not: >> >> ruby-1.9.2-p136 :106 > string = 'David' >> => "David" >> ruby-1.9.2-p136 :107 > arr = [string] >> => ["David"] >> ruby-1.9.2-p136 :108 > arr.each {|s| s = 'new val'} >> => ["David"] >> ruby-1.9.2-p136 :109 > string >> => "David" >> >> > In the first case, you explicitly changed the value of the local variable > str... it didn't change the array contents. In the second case you only > changed the value inside the scope of the block that was enumerating > through. Whether you created the string with String.new or not won't make a > difference. > > Oh, right, I see my errror > Ruby does pass object by reference, but when you do s = "whatever" in the > block, you're creating a new local variable that only lives as long as the > scope of the block. > > If you want to modify an array of strings, for example, you could do: > > arr = ["John", "Doe"] > => ["John","Doe"] > arr.each{|s| s.replace("blah") } > => ["blah","blah"] > > s.replace actually modifies the object, instead of creating a new one. > Perfect, now I think I've got it, thanks! > > > >> I thought that doing >> >> str = 'David' >> >> was just a shortcut to doing >> >> str = String.new('David') >> >> But apparently the behavior at least in the context of an array is >> different. Wow! >> > >> >> >>> >>> > >>> > Excuse my ingenuity, but I am trying to understand... if I have an >>> array of >>> > variables it seems that when the array is created, the elements which >>> were >>> > variables are substituted by values, and there is no reference: >>> >>> >>> > (rdb:1) arr = [v1,v2,v3] >>> > [1, 2, 3] >>> >>> Without resorting to dirty tricks, you can't change the values of >>> local variables other than by actually doing >>> v1 = 2. arr does NOT contain [v1,v2,v3]. It contains 3 objects, and >>> the local variables v1,v2,v3 just happen to also be referencing those >>> same objects. >>> >>> Fred >>> >>> > (rdb:1) v1 >>> > 1 >>> > (rdb:1) arr[0]=5 >>> > 5 >>> > (rdb:1) v1 >>> > 1 >>> > >>> > This must sound like kindergarten but apparently I have been working >>> albeit >>> > successfully under some very false premises. >>> > >>> > >>> > >>> > >>> > >>> > > Fred >>> > >>> > > -- >>> > > You received this message because you are subscribed to the Google >>> Groups >>> > > "Ruby on Rails: Talk" group. >>> > > To post to this group, send email to >>> [email protected]. >>> > > To unsubscribe from this group, send email to >>> > > [email protected]. >>> > > For more options, visit this group at >>> > >http://groups.google.com/group/rubyonrails-talk?hl=en. >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "Ruby on Rails: Talk" group. >>> To post to this group, send email to [email protected]. >>> To unsubscribe from this group, send email to >>> [email protected]. >>> For more options, visit this group at >>> http://groups.google.com/group/rubyonrails-talk?hl=en. >>> >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "Ruby on Rails: Talk" group. >> To post to this group, send email to [email protected]. >> To unsubscribe from this group, send email to >> [email protected]. >> For more options, visit this group at >> http://groups.google.com/group/rubyonrails-talk?hl=en. >> > > -- > You received this message because you are subscribed to the Google Groups > "Ruby on Rails: Talk" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/rubyonrails-talk?hl=en. > -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. 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