Re: [ANN] Lua 5.4.0 (work1) now available
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- Subject: Re: [ANN] Lua 5.4.0 (work1) now available
- From: "Soni \"They/Them\" L." <fakedme@...>
- Date: 2018年3月14日 19:47:32 -0300
On 2018年03月14日 11:11 AM, Roberto Ierusalimschy wrote:
I mean: if I can pass something to a function, and I can get it back from a
call... well it is a value!
That is true. But you cannot pass 'undef' to a function or return
an 'undef' from a function (anymore than you can pass 'while' to a
function).
-- Roberto
Shouldn't undef just expose the C LUA_TNONE to Lua + some neatness?
With the restrictions that it can only be used as arguments, table
values, or to undefine locals (non-lexical or semi-lexical variable
scoping).
string.sub("hello", undef, 3) -- would return "hel"
t[i] = undef -- would erase t[i]
-- non-lexical variable scoping
x = 1
local x = 2
do
x = undef
assert(x == 1)
local x, x, x = 3, 4, 5
assert(x == 5)
x = undef
assert(x == 4)
x = undef
assert(x == 3)
x = undef
assert(x == 1)
end
assert(x == 2)
-- (this can also be made to work with upvalues obviously. at the end it
just undefines the global.)
--
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