Re: [feature request] how about modify the `table.unpack` function to make `table.unpack(table.pack(f()) === f()` equivalent

["Gary V. Vaughan" <gary@...>]

> On Jan 4, 2017, at 8:09 AM, Soni L. <fakedme@gmail.com> wrote:
> 
> On 04/01/17 12:06 PM, Gary V. Vaughan wrote:
>>> On Jan 4, 2017, at 4:32 AM, Soni L. <fakedme@gmail.com> wrote:
>>> 
>>>> On 04/01/17 02:24 AM, 聂威 wrote:
>>>> dear list,
>>>> 
>>>> I have noticed that `table.unpack(list [,i [, j]])` will NOT regards the `n` field in the `list` table,
>>>> 
>>>> I know I can write it like this:
>>>> 
>>>> ```
>>>> table.unpack(list, 1, list.n)
>>>> ```
>>>> 
>>>> but will it be a good idea to make it read `n` field in table.unpack?
>>>> 
>>>> thanks and happy new year!
>>>> 
>>>> ps:
>>>> 
>>>> table.pack in Lua 5.3 manual:
>>>> 
>>>> ```
>>>> 
>>>> 
>>>>      |table.pack (···)|
>>>> 
>>>> Returns a new table with all parameters stored into keys 1, 2, etc. and with a field "|n|" with the total number of parameters. Note that the resulting table may not be a sequence.
>>>> 
>>>> ```
>>> Here's a better idea:
>>> 
>>> Why not make table.pack return a table, the value 1, and the total number of parameters?
>>> 
>>> That way, table.unpack(table.pack(f())) is equivalent to f().
>> But why? There is no practical reason to immediately unpack what was just packed. At some point you need to access the packed values.
>> 
>> Consider:
>> 
>>    local args, from, to = table.pack(...)
>>    -- or argsvalues = table.pack(table.pack(...))?
>>    -- or argstable = {table.pack(...)}?
>>    local r = {n=from}
>>    for i = from, to do
>>      r[i] = process(args[i])
>>    end
>> 
>> versus, IMHO clearer:
>> 
>>    local args = table.pack(...)
>>    local r = {n=args.n}
>>    for i = 1, args.n do
>>       r[i] = args[i]
>>    end
>> 
>> Cheers,
>> Gary
>> 
> 
> t, 1, n is more useful than t, t.n for functions that take a table, a start and an end.
> 
> process(table.pack(...)) vs local t = table.pack(...) process(t, 1, t.n)

Interesting. It would certainly allow for designing your APIs in a different style.  

> Would also be nicer if the standard table library were object-oriented:
> 
> table.sorter(function(a, b) return b < a end)(table.pack(...)) -- auto-sort args

 function table.sorter(comparator)
    return function(argu)
      table.sort(argu, comparator)
      return argu
    end
  end

> table.concater(" | ")(table.pack(...)) -- auto-concat args
> io.write(table.concater("\t")

  function table.concater(separator)
    return function(argu)
      return table.concat(argu, separator)
    end
  end

> (processtostring(table.pack(...))),"\n") -- print(...) implementation, where processtostring calls tostring on every element

  function processtostring(argu)
    local r = {}
    for i = 1, argu.n do
      r[i] = tostring(argu[i])
    end
    return r
  end

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