[ruby-core:47609] Re: [ruby-trunk - Feature #6668] Multiple assignment should not return an Array object

On Wed, Sep 19, 2012 at 3:38 AM, SASADA Koichi <[e-mail]> wrote:
> FYI, from 1.9 the Array for RHS is not generated if it is not needed.
>
> # not generated
> a, b = c, d
> a, b, c = d, e

system ~/projects/jruby $ ruby-1.9.3 -e "def foo(c, d); a, b = c, d;
end; p foo 1, 2"
[1, 2]

system ~/projects/jruby $ ruby-1.9.3 -e "def foo(d, e); a, b, c = d,
e; end; p foo 1, 2"
[1, 2]

Perhaps by not needed you mean "not used in an expression"?

> # generated
> a = b, c
> a = b, c, d
>
> I remain the spec because of compatibility.
> #=> go to matz issue.
>
> As you say the case which need to generate an array are not major case,
> it is not performance problem in my opinion.

I disagree. For example, the following case would make instance
variable initialization much cheaper if the array did not have to be
constructed:

def initialize(a, b, c)
  @a, @b, @c = a, b, c
end

As above, since this line is the return value from the method, an
array would be created that nobody ever uses. There are many similar
cases where multiple assignment just happens to be the last line of a
method but nobody cares about the Array result...so it is wasted
effort to create it.

- Charlie