Re: block-scope finalization

[Sean Conner <sean@...>]

It was thus said that the Great Roberto Ierusalimschy once stated:
> What is wrong with the following proposal?
> 
>   local <some mark to be invented> name = exp
> 
> Unlike a regular 'local' declaration, this one must define only one
> variable and it must be initialized. (Both restrictions could be easily
> removed; they are more about programming style.)
> 
> When the local 'name' goes out of scope, then:
> 
> 1 - if its value is a function, that function is called (no parameters)

  I don't think this is a good idea.  For example:

	do
	  local magic print = print -- because I heard this was faster!

	  print("hello")
	  print("goodbye")
	end

  print() gets called an extra time and an extraneous line of output is
generated.  I purposely picked a function I know has a side effect when no
parameters are called to show the issue here.  We don't know *which*
functions will be assigned to a local value.  So now what?

	do
	  local magic print = print
	  print("hello")
	  print("goodbye")
	  print = nil -- WTF?  
	end

  Another issue---how to __call and __close interact?  

	do
	  local magic foo = {}
	  setmetatable(foo,{ __call = function(self) ... end })

	  foo(3)
	end

foo has call semantics, so is it

	foo(nil)

or

	getmetatable(foo).__close(foo)

  Yes, it might seem clear that __close() happens because foo is a table,
but a reasonable case might be made for the confusion.

> 2 - if its value is a table/userdata, its __close (or some other new
> name) metamethod, if present, is called.

  This I don't have an issue with.

  -spc