# On parallel assignment **URL:** \ **Category:** ruby-talk\ **Created:** [11 January 2006 14:29 UTC](https://rubytalk.org/t/on-parallel-assignment/24029 "2006-01-11T14:29:52Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![Christer\_Nilsson](https://avatars.discourse-cdn.com/v4/letter/c/5fc32e/32.png) [@Christer\_Nilsson](https://rubytalk.org/u/Christer_Nilsson)\ **Post date:** [11 January 2006 14:29 UTC](https://rubytalk.org/t/on-parallel-assignment/24029/1 "2006-01-11T14:29:52Z")
The parallel assignment syntax [a,b] = [c,d] is not allowed I have to write a, b = [c,d] Going deeper [a, [b, c]] = [1, [2, 3]] is not allowed I have to write a, (b, c) = [1, [2, 3]] I'm sure there is a good reason these constructs are disallowed. Can somebody enlighten me? Christer > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Robert](https://avatars.discourse-cdn.com/v4/letter/r/e95f7d/32.png) [@Robert](https://rubytalk.org/u/Robert)\ **Post date:** [11 January 2006 14:58 UTC](https://rubytalk.org/t/on-parallel-assignment/24029/2 "2006-01-11T14:58:04Z")
Christer Nilsson wrote: > The parallel assignment syntax > [a,b] = [c,d] is not allowed The left side is an array constructor. In other words: take value of a and value of b and create a two element array. There is no assignment here. You cannot create an array on the left side of an assignment and try to assign to it: > > =[1,2] SyntaxError: compile error (irb):38: syntax error =[1,2]    ^         from (irb):38         from ❤:0 > > Array.new = [1,2,3] NoMethodError: undefined method `new=' for Array:Class         from (irb):39         from ❤:0 > > (Array.new) = [1,2,3] SyntaxError: compile error (irb):40: syntax error (Array.new) = [1,2,3]              ^         from (irb):40         from ❤:0 > I have to write > a, b = [c,d] I prefer > > a,b=1,2 =\> [1, 2] > > a =\> 1 > > b =\> 2 > Going deeper > [a, [b, c]] = [1, [2, 3]] is not allowed > > I have to write > a, (b, c) = [1, [2, 3]] You can as well do > > a,(b,c)=1,[2,3] =\> [1, [2, 3]] > > a =\> 1 > > b =\> 2 > > c =\> 3 The outermost array is implicit but you must create nested arrays explicitely. > I'm sure there is a good reason these constructs are disallowed. > Can somebody enlighten me? Hope so... Kind regards     robert ---
**Author:** ![David\_Vallner](https://avatars.discourse-cdn.com/v4/letter/d/eb9ed0/32.png) [@David\_Vallner](https://rubytalk.org/u/David_Vallner)\ **Post date:** [11 January 2006 15:36 UTC](https://rubytalk.org/t/on-parallel-assignment/24029/3 "2006-01-11T15:36:51Z")
Christer Nilsson wrote: > The parallel assignment syntax > [a,b] = [c,d] is not allowed > > I have to write > a, b = [c,d] > > Going deeper > [a, [b, c]] = [1, [2, 3]] is not allowed > > I have to write > a, (b, c) = [1, [2, 3]] > > I'm sure there is a good reason these constructs are disallowed. > Can somebody enlighten me? > > Christer You should check out one of the websites that list upcoming syntax changes in Ruby 2.0 - parallel assignment is undergoing relatively significant changes to weed out possible ambiguity when it's used. As well as nested parallel assignment is concerned, I'd say avoid - it's potentially a very confusing construct, and makes your intent unclear. Arrays usually imply the storing of values of homogenous type and purpose - when used in parallel assignment, it means you're most probably not using them that way, and should probably use a different data structure to store the information to make your code easier to understand. David Vallner