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
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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 allowedI 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
Christer Nilsson wrote:
The parallel assignment syntax
[a,b] = [c,d] is not allowedI have to write
a, b = [c,d]Going deeper
[a, [b, c]] = [1, [2, 3]] is not allowedI 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