Re: Why Lua table pairs iteration doesn't hold the last key's position in Node[] ?
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- Subject: Re: Why Lua table pairs iteration doesn't hold the last key's position in Node[] ?
- From: Robert Burke <sharpobject@...>
- Date: Fri, 9 Oct 2020 04:03:28 +0900
On Fri, Oct 9, 2020 at 3:41 AM 张伟智 <robotkzhang@gmail.com> wrote:
> why pairs doesn't return a C closure with an integer upvalue to hold
> the last key's position in Node[] ?
Is there a useful notion of a "C closure" that could be used for this?
It needs to free the associated integer when it is GCed.
The issue you point out is one reason that the iterator protocol could
be improved by separating the first user-visible value in the generic
for loop from the control variable.
That is, instead of being equivalent to this code:
do
local _f, _s, _var = explist
while true do
local var_1, ... , var_n = _f(_s, _var)
_var = var_1
if _var == nil then break end
block
end
end
A loop declaration like
for var_1, ..., var_n in explist do block end
should perhaps be equivalent to this code:
do
local _f, _s, _c = explist
while true do
local _c, var_1, ... , var_n = _f(_s, _var)
if _c == nil then break end
block
end
end