Re: [ANN] Lua 5.4.0 (work1) now available

["Soni \"They/Them\" L." <fakedme@...>]

On 2018-03-17 04:21 AM, Philipp Janda wrote:
> Am 14.03.2018 um 18:17 schröbte Pierre Chapuis:
> > On Wed, Mar 14, 2018, at 15:55, Roberto Ierusalimschy wrote:
> >
> > > Every year or so the list has its recurrent discussion about the length
> > > operator and holes in sequences. Quite often, this discussion leads 
> > > some
> > > people to propose that Lua needs an array type, different from tables.
> >
> > In practice, this is not the reason why people (at least me, but not 
> > only)
> > wish Lua had an array type.
> >
> > The main reason is that Lua is a dynamic language where you can
> > inspect the type of values (with type() mostly), but there is no
> > standard way to know if a table is supposed to be a sequence
> > or not when you get it. But in the outside world, things are not
> > tables, they tend to be sequences or map. This causes issues
> > when we try to interact with it using Lua.
>
> Lua can interact with the outside world just fine. You just can't map 
> Lua tables to outside arrays/maps automatically. That's to be 
> expected, because Lua tables are more powerful that arrays/maps 
> combined, and that's a win for Lua. Any serialization library that 
> pretends this automatic mapping is (always) possible is flawed in its 
> interface. Fortunately, library interfaces can be fixed. I'd suggest 
> passing some form of schema/format into the serialization function (I 
> don't like mutating/annotating my data structures with information 
> that you basically only use for one function call). There's no need to 
> water down Lua's data structures for the sake of communicating to the 
> outside world.

I have this really weird idea now of doing something like this:

table.haskey(t, k)
table.strip(t, k)
table.nullify(t, k)
setmetatable(t, {__null=value})

local key = {}
local value = {}
local t = setmetatable(t, {__null=value})
t[key] = value -- equivalent to table.nullify(t, k), but table.nullify 
is meant for when you don't have access to __null/the metatable, perhaps 
because your library code is meant to work with any libs and not a 
specific null-providing lib.
assert(t[key] == nil)
local l = false
for k,v in pairs(t) do
  assert(k == key)
  assert(v == nil)
  l = true
end
assert(l)
assert(#t == 1)

(__null must be non-nil for it to work, obviously, and you don't wanna 
replace __null but it'd just deal with it if you did.)

This gets us great (de)serialization compatibility, and the functions 
can be made to error for tables without __null?

Sure, tables like {1, 2, 3, nil, 4} still have holes, but that's the 
point - it doesn't break backwards compatibility.

> Philipp

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