Re: [ANN] Lua 5.2.0 (beta-rc5) now available

[HyperHacker <hyperhacker@...>]

On Mon, Jul 4, 2011 at 15:58, Alexander Gladysh <agladysh@gmail.com> wrote:
> On Tue, Jul 5, 2011 at 00:19, David Manura <dm.lua@math2.org> wrote:
>> On Mon, Jul 4, 2011 at 3:40 PM, Luiz Henrique de Figueiredo
>> <lhf@tecgraf.puc-rio.br> wrote:
>>> Lua 5.2.0 (beta-rc5) is now available [...]
>>>        - clarifications between 'deprecated' and 'removed'
>
>> This way of removing functions might not be ideal:
>
> I second this.
>
>>  stdin:1: 'popen' not supported
>>  stack traceback:
>>        [C]: in function 'popen'
>>        stdin:1: in main chunk
>>        [C]: in ?
>
> While this one *may* be justified...
>
>>  > setfenv(function()end, {})
>>  stdin:1: deprecated function
>>  stack traceback:
>>        [C]: in function 'setfenv'
>>        stdin:1: in main chunk
>>        [C]: in ?
>
> ...This one, IMO, makes no sense. If it is deprecated, it must work.
> Otherwise it is removed (and replaced with nonsense stub).
>
> My opinion is that there must be a clear way to programmatically
> determine a capability list of the given Lua interpreter. The best way
> to do this — is to actually *remove* removed functions.
>
> Uninitiated Lua 5.2 users would google up the "setfenv, attempted to
> call a nil value" (or whatever) error message, and would get the
> reason why this happens and what to do on the first hit. (One way to
> guarantee this — is to create a quality set question+answer pairs on
> the subject on StackOverflow.)
>
> My 2c,
> Alexander.
>
>

Hm, I was thinking of something like this:
local deleted = setmetatable({}, {
__call = function() error("This function no longer exists") end,
__eq = function(self, other) return not other end,
})

That would allow you to test if the function exists, and still get a
"removed" error if you call it. However it seems __eq doesn't trigger
when comparing to nil...
Of course, you can do "if somefunc == deleted" instead...

-- 
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