From: Wilson Bilkovich <wilsonb@...>
Date: 2006-12-13T05:17:08+09:00
Subject: Re: Assignment method strangeness

On 12/12/06, Ryan Williams <mr.cruft@gmail.com> wrote:
> Assignment methods are weird, and I wish they acted more like regular
> methods.  It seems like they could be, but the parser doesn't properly parse
> the usage.  Let me show you what I mean.
>
> Assignment methods can't take more than one argument:
>
> class Test
>   def d=(a,b)
>     puts "A: #{a}, B: #{b}"
>   end
> end
>
> test.d = 1, 2      #=>ArgumentError: wrong number of arguments (1 for 2)
> test.d = [1, 2]    #=> ArgumentError: wrong number of arguments (1 for 2)
> test.d = *[1, 2]   #=> ArgumentError: wrong number of arguments (1 for 2)
>

Here's what the parse tree looks like for:
test.d = 1
[:attrasgn, [:vcall, :test], :d=, [:array, [:lit, 1]]]

..and for:
test.d = 1,2
[:attrasgn, [:vcall, :test], :d=,
  [:array, [:svalue, [:array, [:lit, 1], [:lit, 2]]]]]

As you can see in the first one.. even a single value passed to an
assignment is parsed as an array. If you need multiple arguments to an
assignment, you have to handle them inside the method body itself.