[LRUG] Ruby question for a change! Why does this happen...

[Evgeny Shadchnev]

When you say foo += [], this means foo = foo + []. The first thing that
Ruby sees is foo on the left hand side. Since it's an assignment, it
implicitly creates a new local variable foo that's nil by default. When it
comes to evaluating the right hand side, foo is a reference to this local
variable, not your method.

I'm not 100% correct that this is exactly what's going on, so please
correct me if I'm wrong.

Best,
Evgeny


On Tue, Jul 1, 2014 at 10:12 AM, Kenneth Lee <kenfodder at gmail.com> wrote:

> Doing some lazy instantiation and come across this oddity, maybe I'm just
> being dense.
>
> $ irb
>
> irb(main):001:0> def foo
>
> irb(main):002:1>   @bar ||= []
>
> irb(main):003:1> end
>
> => :foo
>
> irb(main):004:0> foo
>
> => []
>
> irb(main):005:0> foo += []
>
> NoMethodError: undefined method `+' for nil:NilClass
>
> from (irb):5
>
> from /Users/ken/.rbenv/versions/2.1.1/bin/irb:11:in `<main>'
>
> irb(main):006:0> foo
>
> => nil
>
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