Re: 5.2 feature list?

[Rici Lake <lua@...>]

On 3-Oct-06, at 11:14 AM, Javier Guerra wrote:

> On Tuesday 03 October 2006 9:49 am, David Olofson wrote:
> > I wasn't really aware of this issue at first (haven't designed all
> > that many languages before), and of course, got it wrong in EEL
> > (local by default), did some scripting, realized it was just plain
> > stupid, switched to explicit declarations for everything, and never
> > looked back.
>
> i've read (and agree with) the long and theoretical explanations about 
> why
> local by default is the wrong choice; but could you share any short 
> anecdote
> that convinced you of this?
>
> my point is that a short and simple example might be more convincing 
> than
> the 'real' reasons (and easier to repeat again and again each time 
> this issue
> is mentioned...)


The problem is that without local declarations, you cannot say where 
the variable is local to.

Two simple examples:

-- Restrict the scope of a large temporary. Really dumb,
-- but anything real would take more than 3 lines.
do
  local temp = string.rep(name.." ", 1e7)
  f:write(md5(temp))
end
-- temp is now gone.

-- Example 2: private closed variables
-- Note the lines with *** (doesn't work with "local-by-default")
function bankAccount()
  local balance = 0
  local self = {}
  function self.deposit(x)
    if x >= 0 then
      -- *** What is the scope of balance --
      balance = balance + x
    else
      error "You cannot deposit a negative amount"
    end
  end
  function self.withdraw(x)
    if x <= balance then
      if x >= 0 then
        -- *** What is the scope of balance --
        balance = balance - x
      else
        error "You cannot withdraw a negative amount"
      end
    else
      error "You do not have enough funds to withdraw that amount"
    end
  end
  function self.balance()
    return balance
  end
  return self
end