# Setting attribute via send in Ruby 1.8.6 **URL:** \ **Category:** Ruby\ **Created:** [October 23, 2009, 5:15pm UTC](https://www.ruby-forum.com/t/setting-attribute-via-send-in-ruby-1-8-6/177782 "2009-10-23T17:15:40Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![cmcfab](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/838e76/32.png) [@cmcfab](https://www.ruby-forum.com/u/cmcfab)\ **Post date:** [October 23, 2009, 5:15pm UTC](https://www.ruby-forum.com/t/setting-attribute-via-send-in-ruby-1-8-6/177782/1 "2009-10-23T17:15:40Z")
Using Ruby 1.8.6. I’ve run into an instance in which I’d like to set attributes of an instance using the send method. I’ve looked around, but found nothing, most likely because I’m using the wrong search terms. Example: class A attr\_reader :foo attr\_writer :foo end a = A.new a.send(“foo”, “newval”) I get the following error: “wrong number of arguments (1 for 0) (ArgumentError)” Am I correct in thinking that this is possible, and that I’m just going about it the wrong way? ---
**Author:** ![cmcfab](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/838e76/32.png) [@cmcfab](https://www.ruby-forum.com/u/cmcfab)\ **Post date:** [October 23, 2009, 5:19pm UTC](https://www.ruby-forum.com/t/setting-attribute-via-send-in-ruby-1-8-6/177782/2 "2009-10-23T17:19:46Z")
On Friday 23 October 2009, Charles C. wrote: > | attr\_writer :foo > |going about it the wrong way? > | The method attr\_writer generates has an equal sign appended to the name you give. This means that attr\_writer :foo generates a method called foo=. So, if you want to call it using send, you need to write: a.send(“foo=”, “newval”) I hope this helps Stefano ---
**Author:** ![cmcfab](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/838e76/32.png) [@cmcfab](https://www.ruby-forum.com/u/cmcfab)\ **Post date:** [October 23, 2009, 6:40pm UTC](https://www.ruby-forum.com/t/setting-attribute-via-send-in-ruby-1-8-6/177782/3 "2009-10-23T18:40:34Z")
On Fri, 23 Oct 2009 17:18:22 +0200, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote in [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > On 10/23/2009 05:10 PM, Charles C. wrote: > > > Using Ruby 1.8.6. > > > > I’ve run into an instance in which I’d like to set attributes of an > > instance using the send method. I’ve looked around, but found > > nothing, most likely because I’m using the wrong search terms. [snip example] > > I get the following error: “wrong number of arguments (1 for 0) > > (ArgumentError)” > > > > Am I correct in thinking that this is possible, and that I’m just > > going about it the wrong way? > > Yes. > > … The suspense almost killed me! > 🙂 > > You need to use the _setter_ method with #send - which happens to be > called “foo=” in your case. Ah, now the lightbulb goes off. I should have remembered the convention of having the setter have an equals sign as part of the name. I’m too used to languages that determine which accessor is used based on which side of the assignment it appears rather than actually using a method name to syntactically simulate assignment. Thanks for the help. ---
**Author:** ![cmcfab](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/838e76/32.png) [@cmcfab](https://www.ruby-forum.com/u/cmcfab)\ **Post date:** [October 24, 2009, 9:06am UTC](https://www.ruby-forum.com/t/setting-attribute-via-send-in-ruby-1-8-6/177782/4 "2009-10-24T09:06:52Z")
On Fri, Oct 23, 2009 at 6:40 PM, Charles C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > … > > name. I’m too used to languages that determine which accessor is used > > based on which side of the assignment it appears rather than actually > > using a method name to syntactically simulate assignment. You can achieve what you want if instead of using attr\_writer you roll your own. I remember a discussion in this list regarding something like: class A def a \*args return @a if args.empty? @a = args[0] end end a = A.new a.a #=\> nil a.a 4 #=\> 4 a.a #=\> 4 With this you can do a.send(:a, 4) Jesus. ---
**Author:** ![cmcfab](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/838e76/32.png) [@cmcfab](https://www.ruby-forum.com/u/cmcfab)\ **Post date:** [October 23, 2009, 5:20pm UTC](https://www.ruby-forum.com/t/setting-attribute-via-send-in-ruby-1-8-6/177782/5 "2009-10-23T17:20:56Z")
On 10/23/2009 05:10 PM, Charles C. wrote: > attr\_writer :foo > going about it the wrong way? > Yes. … 🙂 You need to use the _setter_ method with #send - which happens to be called “foo=” in your case. Kind regards robert ---
**Author:** ![cmcfab](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/838e76/32.png) [@cmcfab](https://www.ruby-forum.com/u/cmcfab)\ **Post date:** [October 24, 2009, 11:05am UTC](https://www.ruby-forum.com/t/setting-attribute-via-send-in-ruby-1-8-6/177782/6 "2009-10-24T11:05:41Z")
On 10/24/2009 09:06 AM, Jesús Gabriel y Galán wrote: > > > > nothing, most likely because I’m using the wrong search terms. > > > > The suspense almost killed me! > > > > I’m glad I did not extend the pause even more. 🙂 > You can achieve what you want if instead of using attr\_writer you roll your own. > a.a #=\> nil > a.a 4 #=\> 4 > a.a #=\> 4 > > With this you can do a.send(:a, 4) This also has the added advantage to be easier with #instance\_eval, i.e. you can then do obj = A.new obj.instance\_eval do a 10 end If you had to use a= in the block you would have to write “self.a = 10” in order to prevent recognition of “a” as a local variable. Nevertheless, the general convention is to use a=. Btw, you could even create a custom attr\_accessor method that will create both variants so you can do obj.a # getter obj.a = 10 # setter obj.a(10) # setter Kind regards robert ---
**Author:** ![cmcfab](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/838e76/32.png) [@cmcfab](https://www.ruby-forum.com/u/cmcfab)\ **Post date:** [October 24, 2009, 10:33am UTC](https://www.ruby-forum.com/t/setting-attribute-via-send-in-ruby-1-8-6/177782/7 "2009-10-24T10:33:59Z")
Hello, > Example: > > class A > attr\_reader :foo > attr\_writer :foo > end You can accomplish this is one line with attr\_accessor :foo . I think every poster has said this, but attr\_reader defines: class A def foo @foo end end While attr\_writer defines: class A def foo= value @foo = value end end Hope this helps, Rob