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comp.lang.ruby

Method missing and arrays as arguments..

Kyle Schmitt

4/6/2009 8:35:00 PM

How do you go about passing arrays as arguments to something like
method_missing? I've got a method that takes an array as an argument,
but calling it via method_missing is proving problematic. How do you
deal with arrays in these situations?

def table_row(values)
# values is the list of items in the table row
#....
end

def method_missing(method,*args)
if respond_to?method.to_s[/^add_([^$]+)/,1]
@data<<method(method.to_s[/^add_([^$]+)/,1]).call(*args)
else
super method_missing(method,*args)
end
end


--Kyle
5 Answers

Gary Wright

4/6/2009 9:01:00 PM

0


On Apr 6, 2009, at 4:35 PM, Kyle Schmitt wrote:

> How do you go about passing arrays as arguments to something like
> method_missing? I've got a method that takes an array as an argument,
> but calling it via method_missing is proving problematic. How do you
> deal with arrays in these situations?
>
> def method_missing(method,*args)
> if respond_to?method.to_s[/^add_([^$]+)/,1]
> @data<<method(method.to_s[/^add_([^$]+)/,1]).call(*args)
> else
> super method_missing(method,*args)
> end
> end


I think your problem is in the else clause. It should be:

else
super
end

You don't want to call method_missing explicitly, you'll create an
infinite recursion.

Rick DeNatale

4/6/2009 9:12:00 PM

0

[Note: parts of this message were removed to make it a legal post.]

On Mon, Apr 6, 2009 at 4:35 PM, Kyle Schmitt <kyleaschmitt@gmail.com> wrote:

> How do you go about passing arrays as arguments to something like
> method_missing? I've got a method that takes an array as an argument,
> but calling it via method_missing is proving problematic. How do you
> deal with arrays in these situations?
>
> def table_row(values)
> # values is the list of items in the table row
> #....
> end
>
> def method_missing(method,*args)
> if respond_to?method.to_s[/^add_([^$]+)/,1]
> @data<<method(method.to_s[/^add_([^$]+)/,1]).call(*args)
> else
> super method_missing(method,*args)
> end
> end



I'm not sure exactly what you are trying to do, I'm guessing that if you
send add_table_row(some_array) to an instance, the method_missing will call
table_row and add the result to @data.

The problem isn't the array argument, it's what you are doing in the true
leg of the if.

The first argument to method_missing is not a method, but a symbol. You are
converting this symbol to a string, stripping off add_ from the beginning
and they trying to call the string, which ain't gonna work.

Instead you want to use send:

class SomeClass
attr_reader :data

def table_row(values)
# values is the list of items in the table row
#....
values
end

def method_missing(symbol,*args)
without_add = symbol.to_s[/^add_([^$]+)/,1]
if respond_to? without_add
@data ||= []
@data<< send(without_add, *args)
else
super method_missing(method,*args)
end
end
end

sc = SomeClass.new
sc.add_table_row([1,2,3])
sc.data # => [[1, 2, 3]]

I used lazy initialization to initialize @data, assuming that this is
vaguely what you are after.

--
Rick DeNatale

Blog: http://talklikeaduck.denh...
Twitter: http://twitter.com/Ri...
WWR: http://www.workingwithrails.com/person/9021-ric...
LinkedIn: http://www.linkedin.com/in/ri...

Rick DeNatale

4/6/2009 9:14:00 PM

0

[Note: parts of this message were removed to make it a legal post.]

On Mon, Apr 6, 2009 at 5:00 PM, Gary Wright <gwtmp01@mac.com> wrote:

>
> On Apr 6, 2009, at 4:35 PM, Kyle Schmitt wrote:
>
> How do you go about passing arrays as arguments to something like
>> method_missing? I've got a method that takes an array as an argument,
>> but calling it via method_missing is proving problematic. How do you
>> deal with arrays in these situations?
>>
>> def method_missing(method,*args)
>> if respond_to?method.to_s[/^add_([^$]+)/,1]
>> @data<<method(method.to_s[/^add_([^$]+)/,1]).call(*args)
>> else
>> super method_missing(method,*args)
>> end
>> end
>>
>
>
> I think your problem is in the else clause. It should be:
>
> else
> super
> end
>
> You don't want to call method_missing explicitly, you'll create an infinite
> recursion.
>
>
Well, that's another problem, which I overlooked in MY response.

--
Rick DeNatale

Blog: http://talklikeaduck.denh...
Twitter: http://twitter.com/Ri...
WWR: http://www.workingwithrails.com/person/9021-ric...
LinkedIn: http://www.linkedin.com/in/ri...

Kyle Schmitt

4/6/2009 10:05:00 PM

0

Ok, I found my issue, it was rather dense of me to be honest, it had
to do with how I was calling it.

That said, this is what I came up with


def method_missing(method,*args)
without_add=method.to_s[/^add_([^$]+)/,1]
if not(without_add.empty?) and respond_to?without_add
#calling the string worked (I'm guessing it tries a .to_sym)
#@data<<method(without_add).call(*args)
# Still, this is prettier
@data<<send(without_add,*args)
else
super
end
end

Kyle Schmitt

4/7/2009 5:37:00 PM

0

Oh, and I forgot to say, thanks, it did help a ton.