# Optional Message Parameters? **URL:** \ **Category:** Ruby\ **Created:** [April 20, 2006, 11:48pm UTC](https://www.ruby-forum.com/t/optional-message-parameters/58372 "2006-04-20T23:48:56Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [April 20, 2006, 11:48pm UTC](https://www.ruby-forum.com/t/optional-message-parameters/58372/1 "2006-04-20T23:48:56Z")
(Warning: Newbie Altert!) How do I write a method with optional params? I would think that this: def do\_this(opt1="", opt2="") puts opt2 end do\_this(opt2=“This”) Would result in “This” being displayed. Instead, “This” becomes the value of opt1. I’d like to set opt1 and opt2 to default to “”. How do I do that? ---
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [April 20, 2006, 11:54pm UTC](https://www.ruby-forum.com/t/optional-message-parameters/58372/2 "2006-04-20T23:54:01Z")
Nathan O. wrote: > (Warning: Newbie Altert!) > > How do I write a method with optional params? I would think that this: > > def do\_this(opt1="", opt2="") > puts opt2 > end > do\_this(opt2=“This”) > > Would result in “This” being displayed. Instead, “This” becomes the > value of opt1. I’d like to set opt1 and opt2 to default to “”. How do I > do that? > Use a hash: def do\_this( args ) puts args[:opt2] end do\_this :opt2=\>“This” #=\> This What you’re doing now is assigning to opt2 then passing it: do\_this(opt2=“This”) puts opt2 #=\> “This” ---
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [April 20, 2006, 11:57pm UTC](https://www.ruby-forum.com/t/optional-message-parameters/58372/3 "2006-04-20T23:57:07Z")
> Use a hash: > > def do\_this( args ) > puts args[:opt2] > end > do\_this :opt2=\>“This” #=\> This > > What you’re doing now is assigning to opt2 then passing it: > > do\_this(opt2=“This”) > puts opt2 #=\> “This” I understand that this will work, but seems so inelegant. Is it really how this is supposed to be done? ---
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [April 21, 2006, 12:01am UTC](https://www.ruby-forum.com/t/optional-message-parameters/58372/4 "2006-04-21T00:01:51Z")
On 4/20/06, Nathan O. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Would result in “This” being displayed. Instead, “This” becomes the > value of opt1. I’d like to set opt1 and opt2 to default to “”. How do I > do that? This is usually a case where you either use \* or a hash parameter. \* is good for cases where you can distinguish by value. In your case it looks like a hash would be appropriate. def do\_this(opts) puts opt[:two] end do\_this(:two =\> “This”) Notes: The hash parameter will always be the last parameter (ignoring & args and other odd parameter changes when using super). This means you can pass many things along side the hash, though the more you add the more complex it gets to manage the interface. Rails uses this technique heavily. Have a look at the find() code in ActiveRecord sometime to learn how they manage such an interface (much cleaner in more recent releases). Future major versions of Ruby are going to have actual named parameters. So much to look forward to in 2.0! Brian. ---
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [April 21, 2006, 12:02am UTC](https://www.ruby-forum.com/t/optional-message-parameters/58372/5 "2006-04-21T00:02:26Z")
Nathan O. wrote: > > Use a hash: > > > > def do\_this( args ) > > puts args[:opt2] > > end > > do\_this :opt2=\>“This” #=\> This > > > > What you’re doing now is assigning to opt2 then passing it: > > > > do\_this(opt2=“This”) > > puts opt2 #=\> “This” > > I understand that this will work, but seems so inelegant. Is it really > how this is supposed to be done? There are default values too: def do\_this( opt1, opt2="" ) puts opt2 end If that’s what you mean. ---
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [April 21, 2006, 12:07am UTC](https://www.ruby-forum.com/t/optional-message-parameters/58372/6 "2006-04-21T00:07:50Z")
Brian M. wrote: > On 4/20/06, Nathan O. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > Would result in “This” being displayed. Instead, “This” becomes the > > value of opt1. I’d like to set opt1 and opt2 to default to “”. How do I > > do that? > > This is usually a case where you either use \* or a hash parameter. \* > is good for cases where you can distinguish by value. In your case it > looks like a hash would be appropriate. > > def do\_this(opts) > puts opt[:two] > end > > do\_this(:two =\> “This”) \*? I don’t even know how I’d google that 🙂 > Notes: The hash parameter will always be the last parameter (ignoring > & args and other odd parameter changes when using super). This means > you can pass many things along side the hash, though the more you add > the more complex it gets to manage the interface. Rails uses this > technique heavily. Have a look at the find() code in ActiveRecord > sometime to learn how they manage such an interface (much cleaner in > more recent releases). _Woosh!_ That was the sound of this discussion going over my head at Mach 2! > Future major versions of Ruby are going to have actual named > parameters. So much to look forward to in 2.0! Definitely looking forward to that! ---
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [April 21, 2006, 12:18am UTC](https://www.ruby-forum.com/t/optional-message-parameters/58372/7 "2006-04-21T00:18:34Z")
> \*? I don’t even know how I’d google that 🙂 The star is used to have fun with parameters. Watch: def have\_fun(\*args) args.each{|arg| puts arg} end have\_fun 1, 2, 3 # outputs 1, 2, 3 It basically takes any additional parameters provided and puts it into an array (with the exception of blocks): def some\_args( opt1, opt2, \*otheropts ) otheropts end some\_args nil, nil, “have”, “fun” # =\> [“have”, “fun”] You can use it the other way to: arguments = [“Hello”, “world”] send(“puts”, \*arguments) # Outputs the arguments See [http://redhanded.hobix.com/bits/wonderOfTheWhenBeFlat.html](http://redhanded.hobix.com/bits/wonderOfTheWhenBeFlat.html) for creative uses. ---
**Author:** ![nko](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/n/91b2a8/32.png) [@nko](https://www.ruby-forum.com/u/nko)\ **Post date:** [April 23, 2006, 6:57am UTC](https://www.ruby-forum.com/t/optional-message-parameters/58372/8 "2006-04-23T06:57:54Z")
On 4/20/06, Nathan O. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Would result in “This” being displayed. Instead, “This” becomes the > value of opt1. I’d like to set opt1 and opt2 to default to “”. How do I > do that? Nathan, looks like you’re expecting Ruby to be like Python, but Ruby doesn’t have keyword args – it just looks at the order of the stuff pass in to a method, and assigns them to the method parameters in that order. In the method call you show above (do\_this(opt2=“This”)), what’s happening (I think) is that some local variable named opt2 (local to the arg list?) is being created in your argument list, and then the string “This” is being assigned to it. Then, after that business is done being evaluated, that string gets passed into the method where it’s assigned to parameter opt1.