# Capture variable arguments

**URL:** <https://www.ruby-forum.com/t/capture-variable-arguments/123082>\
**Category:** Rails\
**Created:** [December 13, 2007, 10:15pm UTC](https://www.ruby-forum.com/t/capture-variable-arguments/123082 "2007-12-13T22:15:28Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![kelleysislander](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kelleysislander](https://www.ruby-forum.com/u/kelleysislander)\
**Post date:** [December 13, 2007, 10:15pm UTC](https://www.ruby-forum.com/t/capture-variable-arguments/123082/1 "2007-12-13T22:15:28Z")

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Without spending several pages trying to explain myself, I have a need  
to do something like this:

def method\_missing(method\_name, \*parameters)  
@method\_name = method\_name  
@parameters = parameters  
end

. . . many lifetimes later:

send(@method\_name, @parameters)

This sorta works - except that @parameters is, rather than a  
collection of bare parameters, an array containing them, which the  
method being called via send() is not expecting. I’m unsure how to  
pull all the contents out of @parameters and make each an individual  
bare argument to pass in send(), and very importantly, not pass  
anything there if @parameters is empty.

Any ideas?

I know this may seem like a weird thing to be trying to do, but it’s  
necessary. Trying to explain why I need to do this would literally  
take several pages of text. I’m hoping I can avoid the “you shouldn’t  
be trying to do this” argument and just figure out a way to do it. 🙂

-Bill

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**Author:** ![kelleysislander](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kelleysislander](https://www.ruby-forum.com/u/kelleysislander)\
**Post date:** [December 13, 2007, 10:29pm UTC](https://www.ruby-forum.com/t/capture-variable-arguments/123082/2 "2007-12-13T22:29:04Z")

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> send(@method\_name, @parameters)

Try send(@method\_name, \*@parameters)

- donald

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<div class="post-metadata">

**Author:** ![kelleysislander](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kelleysislander](https://www.ruby-forum.com/u/kelleysislander)\
**Post date:** [December 13, 2007, 10:34pm UTC](https://www.ruby-forum.com/t/capture-variable-arguments/123082/3 "2007-12-13T22:34:57Z")

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That did it. Thanks so much!

On Dec 13, 4:28 pm, “Ball, Donald A Jr (Library)”

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<div class="post-metadata">

**Author:** ![kelleysislander](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kelleysislander](https://www.ruby-forum.com/u/kelleysislander)\
**Post date:** [December 13, 2007, 10:56pm UTC](https://www.ruby-forum.com/t/capture-variable-arguments/123082/4 "2007-12-13T22:56:10Z")

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> Try send(@method\_name, \*@parameters)

Oh, wow - so \* turns an array into a list of arguments? I can’t find a  
reference to this behavior. Pickaxe talks about using \* with array  
arguments, which is the opposite, isn’t it?

Can you tell me where I could find more about this usage?

///ark

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<div class="post-metadata">

**Author:** ![kelleysislander](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kelleysislander](https://www.ruby-forum.com/u/kelleysislander)\
**Post date:** [December 14, 2007, 4:04pm UTC](https://www.ruby-forum.com/t/capture-variable-arguments/123082/5 "2007-12-14T16:04:24Z")

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On 12/13/07, Ball, Donald A Jr (Library) [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> situation the poster described - when you’re trying to pass a list of  
> arguments to a method that allows a variable number of arguments as  
> discrete arguments intstead of list.

Actually, the \* here (David A. Black calls it the “unary unarray  
operator”) is really a feature of Ruby’s parallel assignments.

```
 a, b = 1, 2

```

Parameter passing in Ruby works just like parallel assignment from the  
actual parameters to the formals.

Now where does \* fit in. You can use it on either the right or left  
hand side of a parallel assignment, for example:

```
a, b = *[1, 2]

```

sets a to 1 and b to 2. Where

```
*a = 1, 2

```

sets a to [1, 2]

and on the left hand side you can have both one or more variables, and  
a final “splatted” one.

```
a, b, *c = *(1..5)

```

sets a to 1, b to 2, and c to [3,4,5]

Note that the \* implicitly converts what follows to an array if  
possible, in Ruby 1.8.x this is done using the to\_ary method if the  
object implements it, in Ruby 1.9 a new to\_splat method is used which  
implemented in fewer classes, so fewer values get converted.

–  
Rick DeNatale

My blog on Ruby  
[http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)

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<div class="post-metadata">

**Author:** ![kelleysislander](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/k/f6c823/32.png) [@kelleysislander](https://www.ruby-forum.com/u/kelleysislander)\
**Post date:** [December 13, 2007, 11:41pm UTC](https://www.ruby-forum.com/t/capture-variable-arguments/123082/6 "2007-12-13T23:41:18Z")

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> > Try send(@method\_name, \*@parameters)
> 
> Oh, wow - so \* turns an array into a list of arguments? I  
> can’t find a reference to this behavior. Pickaxe talks about  
> using \* with array arguments, which is the opposite, isn’t it?
> 
> Can you tell me where I could find more about this usage?

Not specifically, but as I recall, its usage is restricted just to the  
situation the poster described - when you’re trying to pass a list of  
arguments to a method that allows a variable number of arguments as  
discrete arguments intstead of list.

- donald