Re: 'with' statement

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

2016-03-14 4:31 GMT+02:00 Daurnimator <quae@daurnimator.com>:
>
> On 14 Mar 2016 04:25, "Dirk Laurie" <dirk.laurie@gmail.com> wrote:
>>
>> Thanks to everyone who replied. The present protocol is:
>>
>> --- with(tbl[,context])
>> -- Creates a new table with write access to `tbl` and read access to
>> --   `tbl` and `context`, which defaults to `_ENV`. If current _ENV
>> --   is local or an upvalue, it must be explicitly given as `context`.
>> --   If really no context is required, specify an explicit `nil`.
>> -- Designed for the idiom
>> --    do local _ENV=with(tbl)
>> --      ...
>> --    end
>> -- which mimics the `with` keyword in Pascal, Visual Basic etc.
>>
>> The code is:
>>
>> local
>> function with(tbl,...)
>>   local context = ...
>>   if select('#',...)==0 then context = _ENV end
>>   if context then
>>     return setmetatable({},{__newindex=tbl,
>>       __index=function(_,key) return tbl[key] or context[key] end})
>>   else
>>     return tbl
>>   end
>> end
>
> The optional context can't default to _ENV, as environments are lexical, and
> will be taken from the _ENV of where `with` is declared.

In an earlier version of the comments, the phrase "which defaults to `_ENV`"
said "which defaults to `_ENV` at the time when `with` is loaded" and the
first paragraph ended there. I thought the issue needed a bit of spelling out
and replaced it by the sentence starting `If current _ENV ...".

It seems that both are needed :-)

Thanks.