Re: More on environments and objects

[Rici Lake <lua@...>]

On 26-Aug-05, at 9:35 AM, Chris Marrin wrote:

> It would not be hard to add something to CallInfo to indicate that 
> this method was called with the SELF instruction. That would no longer 
> allow this:
>
>     instance.g(instance, instance2)
>
> in place of this:
>
>     instance:g(instance2)
>
> but it would still be compatible because I'm making the ':' syntax a 
> requirement in my object system. The rest of Lua works as it always 
> has.
>
> Anyway, does this seem like a reasonable approach?

The problem with this is that sometimes you need to call an instance 
method supplying the actual instance. This shows up at odd moments; the 
simplest example I can think of is the following:

table.foreach calls a function for every k,v in a table. It could be 
written:

function table.foreach(tab, func)
  for k, v in pairs(tab) do
    local rv = func(k, v)
    if rv then return rv end
  end
end

Now, suppose I actually want to invoke an object method, instead of 
calling a function? I could do that with an explicit wrapper:

  table.foreach(tab, function(k, v) return obj:method(k, v) end)

but that would get tedious, so I would want to refactor it:

function table.foreachmeth(obj, tab, method)
  for k, v in pairs(tab) do
    local rv = obj[method](obj, k, v)
    if rv then return rv end
  end
end

table.foreachmeth(obj, t, "send")

I could even introduce that into the object:

obj.foreach = foreachmeth
obj:foreach(tab, "send")

How would I write this if the method refused to execute unless 
self-called? The best I can come up with is filling the method name 
into a template and then compiling the template, which seems yukky.