Re: ipairs in Lua 5.3.0-alpha
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- Subject: Re: ipairs in Lua 5.3.0-alpha
- From: Jan Behrens <jbe-lua-l@...>
- Date: 2014年8月15日 16:54:20 +0200
On 2014年8月15日 15:44:11 +0200
Jan Behrens <jbe-lua-l@public-software-group.org> wrote:
> function alternate_ipairs(t)
> print("Evaluating length here!")
> return alternate_ipairs_aux, t, #t, 0 -- not a triplet but a quadruple
> end
As a matter of taste, it would also be possible to append any extra
state variables to the end of the triplet, rather than inserting them
in the middle:
========================================
function another_for(args)
local f, s, var = table.unpack(args.explist)
local extras = {select(4, table.unpack(args.explist))}
local block = args.block
while true do
local results = {f(s, var, table.unpack(extras))}
if results[1] == nil then break end
var = results[1]
block(table.unpack(results))
end
end
do
local function another_ipairs_aux(t, i, maxn)
if i < maxn then
i = i + 1
return i, t[i]
else
return nil
end
end
function another_ipairs(t)
print("Evaluating length here!")
return another_ipairs_aux, t, 0, #t -- not a triplet but a quadruple
end
end
t = {"a", "b", "c"}
another_for{explist = {another_ipairs(t)}, block = function(i, v)
print(i, v)
end}
-- results in:
-- Evaluating length here!
-- 1 a
-- 2 b
-- 3 c
========================================
For example allowing construct as follows:
========================================
do
local function iterate_aux(t, i, e)
if i < e then
i = i + 1
return i, t[i]
else
return nil
end
end
function iterate_from_to(tbl, from, to)
return iterate_aux, tbl, from - 1, to -- return a quadruple
end
end
t = {"a", "b", "c"}
for i, v in iterate_from_to(t, 1, 2) do
print(i, v)
end
-- would print:
-- 1 a
-- 2 b
========================================
Regards
Jan