# Syntax questions **URL:** \ **Category:** Ruby\ **Created:** [February 22, 2006, 3:14am UTC](https://www.ruby-forum.com/t/syntax-questions/71693 "2006-02-22T03:14:48Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![lstrecv](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/e68b1a/32.png) [@lstrecv](https://www.ruby-forum.com/u/lstrecv)\ **Post date:** [February 22, 2006, 3:14am UTC](https://www.ruby-forum.com/t/syntax-questions/71693/1 "2006-02-22T03:14:48Z")
A few simple syntax questions: 1. Anyway to do use the default arg for nonlast params? Something like: run(xyz, , 3) 2. Veru often I see things like: a, b = meth() Is meth returning two objects? Or is it returning one object - like a tuple or something - which the parser automagically splits into a & b? What are the rules of using two vars with commas together? Thanks ---
**Author:** ![lstrecv](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/e68b1a/32.png) [@lstrecv](https://www.ruby-forum.com/u/lstrecv)\ **Post date:** [February 22, 2006, 2:04pm UTC](https://www.ruby-forum.com/t/syntax-questions/71693/2 "2006-02-22T14:04:41Z")
removed\_email\_address@domain.invalid wrote: > A few simple syntax questions: > > 1. Anyway to do use the default arg for nonlast params? Something > like: > run(xyz, , 3) No. You have to use one form of keyword arguments (for example by using a hash). Note that proper support for this is likely to happen in Ruby 2.0. > 1. Veru often I see things like: > a, b = meth() > Is meth returning two objects? Or is it returning one object - like a > tuple or something - which the parser automagically splits into a & b? > What are the rules of using two vars with commas together? It’s a combination of parallel assignment with multiple return values. # parallel assignment a,b,c=1,2,3 a,b,c=[1,2,3] # multiple return values def mu1 return 1,2,3 end def mu2 [1,2,3] end def mu3 return [1,2,3] end irb(main):015:0\> a,b,c = mu1 =\> [1, 2, 3] irb(main):016:0\> a =\> 1 irb(main):017:0\> b =\> 2 irb(main):018:0\> c =\> 3 irb(main):019:0\> a,b,c = mu2 =\> [1, 2, 3] irb(main):020:0\> a =\> 1 irb(main):021:0\> b =\> 2 irb(main):022:0\> c =\> 3 irb(main):023:0\> a,b,c = mu3 =\> [1, 2, 3] irb(main):024:0\> a =\> 1 irb(main):025:0\> b =\> 2 irb(main):026:0\> c =\> 3 The star operator can be used to collect remaining args: irb(main):029:0\> a,\*b = mu1 =\> [1, 2, 3] irb(main):030:0\> a =\> 1 irb(main):031:0\> b =\> [2, 3] More strictly speaking, returning anything that implements #to\_ary will be treated this way: irb(main):032:0\> class Foo irb(main):033:1\> def to\_ary() [“foo”,2,3] end irb(main):034:1\> end =\> nil irb(main):035:0\> def foo() Foo.new end =\> nil irb(main):036:0\> a,b,c = foo =\> [“foo”, 2, 3] irb(main):037:0\> a =\> “foo” irb(main):038:0\> b =\> 2 irb(main):039:0\> c =\> 3 HTH Kind regards ``` robert ``` ---
**Author:** ![lstrecv](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/e68b1a/32.png) [@lstrecv](https://www.ruby-forum.com/u/lstrecv)\ **Post date:** [February 24, 2006, 6:46pm UTC](https://www.ruby-forum.com/t/syntax-questions/71693/3 "2006-02-24T18:46:21Z")
DÅ?a Streda 22 Február 2006 02:33 removed\_email\_address@domain.invalid napísal: > A few simple syntax questions: > > 1. Anyway to do use the default arg for nonlast params? Something > like: > run(xyz, , 3) I don’t think so, would be a PITA to parse / check against typos. Use an options hash when you need funky method invocation forms. > 1. Veru often I see things like: > a, b = meth() > Is meth returning two objects? Or is it returning one object - like a > tuple or something - which the parser automagically splits into a & b? > What are the rules of using two vars with commas together? It’s returning an Array, which is then automagically split in the parallel assignment construct. david@chello082119107152:~$ irb irb(main):001:0\> a, b = [1, 2] =\> [1, 2] irb(main):002:0\> a =\> 1 irb(main):003:0\> b =\> 2 Might possibly change in 1.9 / 2.0 to reduce the ambiguity and general mystery surrounding parallel assignment in strange cases. (Basically, once the number of lvalues and rvalues differs, things get mildly funky, and it’s only downhill from there) David V. ---
**Author:** ![lstrecv](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/e68b1a/32.png) [@lstrecv](https://www.ruby-forum.com/u/lstrecv)\ **Post date:** [February 24, 2006, 6:46pm UTC](https://www.ruby-forum.com/t/syntax-questions/71693/4 "2006-02-24T18:46:23Z")
DÅ?a Streda 22 Február 2006 12:27 Ross B. napísal: > > mystery surrounding parallel assignment in strange cases. (Basically, > > once the number of lvalues and rvalues differs, things get mildly funky, > > and it’s only downhill from there) > > Seriously? If that’s true, I hope it never comes to pass. I don’t think > it’s mysterious, and it’s saved me a good few lines of code here and > there… Hmm, it’s not on eigenclass, so I might have been hallucinating. IIRC, wherever I read about that, the change was related to when the last rvalue, or the only rvalue was an Array - the automagical expansion being removed or some such. Don’t take this with any authority from me though. David V. ---
**Author:** ![lstrecv](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/e68b1a/32.png) [@lstrecv](https://www.ruby-forum.com/u/lstrecv)\ **Post date:** [February 24, 2006, 6:46pm UTC](https://www.ruby-forum.com/t/syntax-questions/71693/5 "2006-02-24T18:46:21Z")
On Wed, 2006-02-22 at 10:50 +0900, David V. wrote: > of lvalues and rvalues differs, things get mildly funky, and it’s only > downhill from there) Seriously? If that’s true, I hope it never comes to pass. I don’t think it’s mysterious, and it’s saved me a good few lines of code here and there… a,b = [1,2,3] # =\> [1, 2, 3] a # =\> 1 b # =\> 2 a,\*b = [1,2,3] # =\> [1, 2, 3] a # =\> 1 b # =\> [2, 3] a,b,c = [1,2] # =\> [1, 2] a # =\> 1 b # =\> 2 c # =\> nil Which is exactly what I expected to happen.