# Multiple values & variable assignment **URL:** \ **Category:** ruby-talk\ **Created:** [8 January 2005 04:31 UTC](https://rubytalk.org/t/multiple-values-variable-assignment/15667 "2005-01-08T04:31:26Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Its\_Me](https://avatars.discourse-cdn.com/v4/letter/i/958977/32.png) [@Its\_Me](https://rubytalk.org/u/Its_Me)\ **Post date:** [8 January 2005 04:31 UTC](https://rubytalk.org/t/multiple-values-variable-assignment/15667/1 "2005-01-08T04:31:26Z")
Why does     def f; 1, 2, 3; end     x,y,z = f give x=1, y=2, z=3 While     x = f gives x=[1, 2, 3]? Also:     x,y=[1, 2], 3 #=\> x=[1,2] and y[3], fine     x,y=[1, 2] #=\> x=1, y=2 : not fine This is inconsistent. Instead I propose:     x,y,z = f #=\> x=1,y=2,z=3 (as current)     x = f #=\> x = 1 (CHANGE)     \*x = f #=\> x=[1, 2, 3] (CHANGE)     x, y = \*f #=\> an error (f on R.h.s. is not an array)     x, y, z = [1, 2, 3], 4, 5 #=\> x=[1, 2, 3], y=4, z=5 (current)     x, y, z = [1, 2, 3] #=\> x=[1, 2, 3], y=nil, z=nil (CHANGE)     \*x = [1, 2, 3] #=\> x = [[1, 2, 3]] (current)     x, y, z = \*[1, 2, 3] #=\> x=1, y=2, z=3 (current) I am trying to write a getter that returns the instance variable + something special if that instance variable has not been initialized. Normal calls would ignore the second return value. The behavior above makes it difficult. Alternatives? Will this continue in 2.0? Thanks. btw: I think arrays and multiple values should be strictly separated syntactic classes. ---
**Author:** ![Robert](https://avatars.discourse-cdn.com/v4/letter/r/e95f7d/32.png) [@Robert](https://rubytalk.org/u/Robert)\ **Post date:** [8 January 2005 13:26 UTC](https://rubytalk.org/t/multiple-values-variable-assignment/15667/2 "2005-01-08T13:26:25Z")
"itsme213" \ schrieb im Newsbeitrag news:WkJDd.9898$ho.9719@fe2.texas.rr.com... > Why does >    def f; 1, 2, 3; end You sure, that this is the code you use? > > def f; 1, 2, 3; end SyntaxError: compile error (irb):49: syntax error def f; 1, 2, 3; end          ^         from (irb):49         from (null):0 I'll use > > def f; return 1, 2, 3; end =\> nil >    x,y,z = f > give x=1, y=2, z=3 > > While >    x = f > gives x=[1, 2, 3]? It's an optimization to save typing: if there are multiple values and on one side there is only one value "\*" is automatically prepended: > > x = f =\> [1, 2, 3] > > x =\> [1, 2, 3] > > x = \*f =\> [1, 2, 3] > > x =\> [1, 2, 3] If you want just the first element you got to do > > x, = f =\> [1, 2, 3] > > x =\> 1 > Also: >    x,y=[1, 2], 3 #=\> x=[1,2] and y[3], fine >    x,y=[1, 2] #=\> x=1, y=2 : not fine > > This is inconsistent. Instead I propose: >    x,y,z = f #=\> x=1,y=2,z=3 (as current) >    x = f #=\> x = 1 (CHANGE) >    \*x = f #=\> x=[1, 2, 3] (CHANGE) >    x, y = \*f #=\> an error (f on R.h.s. is not an array) >    x, y, z = [1, 2, 3], 4, 5 #=\> x=[1, 2, 3], y=4, z=5 (current) >    x, y, z = [1, 2, 3] #=\> x=[1, 2, 3], y=nil, z=nil (CHANGE) >    \*x = [1, 2, 3] #=\> x = [[1, 2, 3]] (current) >    x, y, z = \*[1, 2, 3] #=\> x=1, y=2, z=3 (current) > > I am trying to write a getter that returns the instance variable + something > special if that instance variable has not been initialized. Normal calls > would ignore the second return value. The behavior above makes it difficult. > Alternatives? Will this continue in 2.0? > > Thanks. > > btw: I think arrays and multiple values should be strictly separated > syntactic classes. IMHO we have to judge the costs of this change (broken code, confused coders :-)) vs. what we gain (more consistency). Dunno on what side the balance will come down though. Kind regards     robert ---
**Author:** ![Charles\_Mills1](https://avatars.discourse-cdn.com/v4/letter/c/85f322/32.png) [@Charles\_Mills1](https://rubytalk.org/u/Charles_Mills1)\ **Post date:** [8 January 2005 22:16 UTC](https://rubytalk.org/t/multiple-values-variable-assignment/15667/3 "2005-01-08T22:16:24Z")
Robert Klemme wrote: > "itsme213" \ schrieb im Newsbeitrag > news:WkJDd.9898$ho.9719@fe2.texas.rr.com... > \> Why does > \> def f; 1, 2, 3; end > > You sure, that this is the code you use? > > \>\> def f; 1, 2, 3; end > SyntaxError: compile error > (irb):49: syntax error > def f; 1, 2, 3; end >          ^ >         from (irb):49 >         from (null):0 > > I'll use > > \>\> def f; return 1, 2, 3; end > =\> nil > > \> x,y,z = f > \> give x=1, y=2, z=3 > \> > \> While > \> x = f > \> gives x=[1, 2, 3]? You can think of it as return splat. Looks like Ruby 2.0 will give you piece of mind, see below... > It's an optimization to save typing: if there are multiple values and on one > side there is only one value "\*" is automatically prepended: > > \>\> x = f > =\> [1, 2, 3] > \>\> x > =\> [1, 2, 3] > \>\> x = \*f > =\> [1, 2, 3] > \>\> x > =\> [1, 2, 3] > > If you want just the first element you got to do > > \>\> x, = f > =\> [1, 2, 3] > \>\> x > =\> 1 (...) I think this is the same issue as > def yields > yield(1,2) > end =\> nil > yields { |a| puts a.inspect } (irb):4: warning: multiple values for a block parameter (2 for 1) from (irb):2 [1, 2] =\> nil More info on this here: [http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-dev/23568](http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-dev/23568) I know there is an English version of that post somewhere, but I can't find it on google... -Charlie ---
**Author:** ![Its\_Me](https://avatars.discourse-cdn.com/v4/letter/i/958977/32.png) [@Its\_Me](https://rubytalk.org/u/Its_Me)\ **Post date:** [10 January 2005 01:01 UTC](https://rubytalk.org/t/multiple-values-variable-assignment/15667/4 "2005-01-10T01:01:23Z")
But this is about more than just assignment, it is also about method calls vs. method defs. > \> Why does > \> def f; 1, 2, 3; end > > You sure, that this is the code you use? My mistake, it was: def f; return 1, 2, 3; end > It's an optimization to save typing: if there are multiple values and on one > side there is only one value "\*" is automatically prepended: Ah. Unfortunate decision, because ... x = 1, 2, 3 #=\> x = [1, 2, 3] \*x = 1, 2, 3 #=\> x = [1, 2, 3] def f(x); puts x; end     f(1, 2, 3) #=\> ArgError: wrong num. of args     f([1, 2, 3]) #=\> [1, 2, 3] def g(\*x); puts x; end     g(1, 2, 3) #=\> [1, 2, 3] > \>\> x, = f Ouch! I did not know that. But     def f(x,); end #=\> error. i.e. There is no such ',' syntax for method or proc parameters, just '\*'. Method calls establish bindings. \*, \*\*, and & are nicely consistent and symmetric in     method call: ... f(\*x)         vs.     method definition: def f(\*x); end Since both method call and assignment establish variable bindings, I would suggest that: \* on lhs vs. rhs of assignement should parallel \* on call vs. def \*\* on lhs vs. rhs of assignment (if allowed) should parallel \*\* on call vs. def I'd say the same for '&', but can't think of a meaningful '&x = foo'. > IMHO we have to judge the costs of this change (broken code, confused coders > :-)) vs. what we gain (more consistency). Dunno on what side the balance > will come down though. Imho, a design decision that saves typing a single \*, and as a result makes binding variables via the assigment operation inconsistent with binding variables via a method call, is one that \_should\_ be changed for 2.0. What do other Rubyists think of this proposal (assuming there was no issue of backward compatibility) ? > **···** > > "Robert Klemme" \ wrote ---
**Author:** ![Robert](https://avatars.discourse-cdn.com/v4/letter/r/e95f7d/32.png) [@Robert](https://rubytalk.org/u/Robert)\ **Post date:** [10 January 2005 09:31 UTC](https://rubytalk.org/t/multiple-values-variable-assignment/15667/5 "2005-01-10T09:31:21Z")
"itsme213" \ schrieb im Newsbeitrag news:sskEd.20122$q4.3165@fe1.texas.rr.com... > But this is about more than just assignment, it is also about method calls > vs. method defs. > > \> \> Why does > \> \> def f; 1, 2, 3; end > \> > \> You sure, that this is the code you use? > > My mistake, it was: def f; return 1, 2, 3; end > > \> It's an optimization to save typing: if there are multiple values and on > one > \> side there is only one value "\*" is automatically prepended: > > Ah. Unfortunate decision, because ... > > x = 1, 2, 3 #=\> x = [1, 2, 3] > \*x = 1, 2, 3 #=\> x = [1, 2, 3] > > def f(x); puts x; end >     f(1, 2, 3) #=\> ArgError: wrong num. of args >     f([1, 2, 3]) #=\> [1, 2, 3] > > def g(\*x); puts x; end >     g(1, 2, 3) #=\> [1, 2, 3] > > \> \>\> x, = f > > Ouch! I did not know that. But >     def f(x,); end #=\> error. > i.e. There is no such ',' syntax for method or proc parameters, just '\*'. Yeah: > > def f(x,\*) p x end =\> nil > > f 1,2,3 1 =\> nil > Method calls establish bindings. \*, \*\*, and & are nicely consistent and > symmetric in >     method call: ... f(\*x) >         vs. >     method definition: def f(\*x); end > Since both method call and assignment establish variable bindings, I would > suggest that: > \* on lhs vs. rhs of assignement should parallel \* on call vs. def > \*\* on lhs vs. rhs of assignment (if allowed) should parallel \*\* on call vs. > def I think "\*\*" is already taken: > > -2 \*\* 3 =\> -8 Dunno whether it would be possible to extend the parser with a unary variant of it. > I'd say the same for '&', but can't think of a meaningful '&x = foo'. > > \> IMHO we have to judge the costs of this change (broken code, confused > coders > \> :-)) vs. what we gain (more consistency). Dunno on what side the balance > \> will come down though. > > Imho, a design decision that saves typing a single \*, and as a result makes > binding variables via the assigment operation inconsistent with binding > variables via a method call, is one that \_should\_ be changed for 2.0. I'm not sure whether I agree. After all assignment and method call are not exactly the same although I can see the common issue of variable binding. One of the differences is that the assignment has a result: > > a,b,\*c=1,2,3,4 =\> [1, 2, 3, 4] > > x=(a,b,\*c=1,2,3,4) =\> [1, 2, 3, 4] > > x =\> [1, 2, 3, 4] > What do other Rubyists think of this proposal (assuming there was no issue > of backward compatibility) ? If it wasn't for the backward compatibility issue I think a change would lead to more consistence. At least nothing I see at the moment. Regards     robert > **···** > > > "Robert Klemme" \ wrote