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?
···
--
Charles Calvert | Web-site Design/Development
Celtic Wolf, Inc. | Software Design/Development http://www.celticwolf.com/ | Data Conversion
(703) 580-0210 | Project Management
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
···
On Friday 23 October 2009, Charles Calvert 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.
>
>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?
>
You need to use the _setter_ method with #send - which happens to be called "foo=" in your case.
Kind regards
robert
···
On 10/23/2009 05:10 PM, Charles Calvert 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.
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?
On Fri, 23 Oct 2009 17:18:22 +0200, Robert Klemme
<shortcutter@googlemail.com> wrote in
<7kdvpuF37n3jvU1@mid.individual.net>:
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.
···
On 10/23/2009 05:10 PM, Charles Calvert wrote:
--
Charles Calvert | Web-site Design/Development
Celtic Wolf, Inc. | Software Design/Development http://www.celticwolf.com/ | Data Conversion
(703) 580-0210 | Project Management
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.
···
On Fri, Oct 23, 2009 at 6:40 PM, Charles Calvert <cbciv@yahoo.com> wrote:
On Fri, 23 Oct 2009 17:18:22 +0200, Robert Klemme
<shortcutter@googlemail.com> wrote in
<7kdvpuF37n3jvU1@mid.individual.net>:
On 10/23/2009 05:10 PM, Charles Calvert 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.
On Fri, 23 Oct 2009 17:18:22 +0200, Robert Klemme
<shortcutter@googlemail.com> wrote in
<7kdvpuF37n3jvU1@mid.individual.net>:
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!
I'm glad I did not extend the pause even more.
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.
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)
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
