Re: [ANN] Lua 5.3.0 (work2) now available

[Dirk Laurie <dirk.laurie@...>]

5.2.2: For the unary - and # operators, the metamethod is called with
a dummy second argument.

5.3.0-work2: For the unary minus and the bitwise not operators, the
metamethod is computed and called with a dummy second operand, equal
to the first one.

The length operator has been omitted (but it still is called with a
dummy second argument).

In both cases: This extra argument is only to simplify Lua's
internals; it may be removed in future versions. (For most uses this
extra argument is irrelevant.)

I'd like to argue in favour of changing the policy statement here to:

| This extra argument simplifies Lua's internals, and is irrelevant for
| most uses, but may be exploited by writers of metamethods.

I.e. no threat of its being removed, please!


2014-03-23 7:50 GMT+02:00 Dirk Laurie <dirk.laurie@gmail.com>:
> The 5.2.2 manual spell out the details of metamethods in pseudo-Lua.
> The 5.3-work2 manual only does so in English, which is usually rather
> different from the English of the 5.2.2 manual — understandably so,
> since some things from the pseudo-Lua code now need to be said.
>
> The description of metamethods therefore demands very careful
> reading. So far I've found one subtle linguistic imprecision
> in the new version, the description of __eq.
>
> 5.2.2: A metamethod is selected only when both values being compared
> have the same type and the same metamethod for the selected operation,
> and the values are either tables or full userdata.
>
> 5.3.work2: Lua will try a metamethod only when the values being
> compared are both either tables or full userdata, both have the same
> metamethod, and they are not primitively equal.
>
> 5.2.2 does not say "they are not primitively equal", but the code
> shows it. 5.3.work2 does not say "have the same type", but
> implies it by the word "both" and saying "tables" rather than
> "a table". The point could be made more strongly by a small
> change in the wording:
>
> Lua will try a metamethod only when the values being compared are
> either both tables or both full userdata, both have the same
> metamethod, and they are not primitively equal.
>
>
> 2014-03-21 22:44 GMT+02:00 Luiz Henrique de Figueiredo <lhf@tecgraf.puc-rio.br>:
>> Lua 5.3.0 (work2) is now available for testing at
>>         http://www.lua.org/work/lua-5.3.0-work2.tar.gz
>>
>> MD5     52bd13d0b40f637bc388a133b9bb8771  -
>> SHA1    e52ea0acf4b2d7bf042f48bd01dddc149d517184  -
>>
>> This is a work version. An updated reference manual is included but
>> all details may change in the final version. See
>>         http://www.lua.org/work/doc/readme.html
>>
>> The main change in Lua 5.3.0 is the introduction of integers.
>> For other changes, see
>>         http://www.lua.org/work/doc/readme.html#changes
>>
>> The complete diffs from work1 are at
>>         http://www.lua.org/work/diffs-lua-5.3.0-work1-work2.txt
>>
>> Enjoy. All feedback welcome. Thanks.
>> --lhf
>>
>>