Re: User-definable table length

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

On 2018-03-17 02:40 PM, Egor Skriptunoff wrote:
> On Sat, Mar 17, 2018 at 7:39 PM, Jay Carlson wrote:
>
>     > New syntax {...#} is used for constructing a table
>     > with its "user-specified length" set to actual data length.
>     >
>     > Probably, syntax {...#} is not nice.
>
>     I wonder how much code would break by replacing the existing
>     meaning of #{}.
>     ...
>     For completeness, add the sugar:
>       f#{math.pi} <=> f(#{math.pi})
>
>
> The syntax I suggest is {...#},  not #{...}
> #{...} should have the old meaning, as I don't want to break old Lua code.
> All Lua 5.3 programs would be runnable on Lua 5.4 VM without 
> modifications.
> But in 5.4 new incompatible syntax {...#} would exist for new semantics.
>
> All the discussions about Lua table length issues are in the context 
> of arrays.
> Table length is undefined for dictionaries.
> IMO, only sequential part should be counted for {...#} constructor.
> Example: the length of non-sequence table such as
> { 1, 2, 3, [4]=4, [42]=42 #}
> depending on the implementation, may be 3.
> assert( #{ 1, 2, 3, [4]=4 } == 4)
> assert( #{ 1, 2, 3, [4]=4 #} == 3)

Sparse array, lua 5.3:

setmetatable({1, 2, 3, [42] = 42, n = 42}, nlen)

Sparse array, "egorlua":

{1, 2, 3, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, 
nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, 
nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, 42 #}

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