From: mortee <mortee.lists@...>
Date: 2007-10-12T20:35:02+09:00
Subject: Re: Array +=

Simon Mullis wrote:
>>> (a ||= []) << [1, 2, 3, 4]
> => [[1, 2, 3, 4]]
> 
> But
> 
>>> ( a ||= [] ) += [ 1, 2, 3, 4 ]
> SyntaxError: compile error
> (irb):28: syntax error, unexpected tOP_ASGN, expecting $end
> ( a ||= [] ) += [ 1, 2, 3, 4 ]
>                ^
>         from (irb):28
> 
> Why?
> 
> I guess it's a precedence issue. '<<' is a method in the Array class.
> '+=' is not.

The difference is that << is a method, += is an assignment. (a ||= [])
returns an object, on which you can call a method, but you can't assign
to. You can only assign to the a variable itself, which (a ||= []) is
not. I guess.

mortee