From: Ryan Williams <mr.cruft@...>
Date: 2006-12-13T03:37:32+09:00
Subject: Assignment method strangeness

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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)

Assignment methods can't take blocks:

class Test
  def t=(t, &block)
    @t = t
    block.call
  end
end

test = Test.new
test.t = 5 { puts "block" }   #=> SyntaxError: compile error
                                      #=> parse error, unexpected '{',
expecting $


You can't seem to replace the single required argument with a block:

class Test
  def v=(&block)
    block.call
  end
end

test = Test.new
test.v ={ puts "block" }   #=> Exception: wrong number of arguments (1 for
0)


You can, of course, get around these restrictions with #send

test.send(:d=, 1, 2)     #=> A: 1, B: 2

Though you can define these methods all you want, it seems as though the
parser that does the syntactic sugaring at the call location makes some very
narrow assumptions about the nature of the assignment method.  Is there any
way around this?

-RYaN

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