Correct description of global unpack's parameters

[dv-extrarius]

Correct the description of the unpack parameters.

Changes

The description of unpack's j parameter was wrong. It is not a count, it is the index of the last element to unpack. Updated the description of the i parameter to match the new wording of the j parameter.

Checks

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[IgnisRBX]

I reverted the suggestion of the "j" parameter, which isn't the "index of the last element to unpack", but rather the number of indices to unpack (default to the total number of indices) starting from the given index number "i" (default of the first index).

[dv-extrarius]

I reverted the suggestion of the "j" parameter, which isn't the "index of the last element to unpack", but rather the number of indices to unpack (default to the total number of indices) starting from the given index number "i" (default of the first index).

That's not how it functioned for me in roblox. I had an array and wanted slices so I tried with i=1, 11, 21, etc and j=10 and only the first slice had elements. When I made j=10, 20, 30, etc it functioned as I wanted, slicing 10 elements at a time.

In roblox, this code:

local values = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

local slice1 = {unpack(values, 1, 3)}
print("Slice1 length:", #slice1)

local slice2 = {unpack(values, 4, 3)}
print("Slice2 length:", #slice2)

local slice3 = {unpack(values, 7, 3)}
print("Slice3 length:", #slice3)

produces this output:

Slice1 length: 3  -  Server - Script:4
Slice2 length: 0  -  Server - Script:7
Slice3 length: 0  -  Server - Script:10

whereas this code in roblox:

local values = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

local slice1 = {unpack(values, 1, 3)}
print("Slice1 length:", #slice1)

local slice2 = {unpack(values, 4, 6)}
print("Slice2 length:", #slice2)

local slice3 = {unpack(values, 7, 9)}
print("Slice3 length:", #slice3)

produces

Slice1 length: 3  -  Server - Script:4
Slice2 length: 3  -  Server - Script:7
Slice3 length: 3  -  Server - Script:10

which shows j is not, in fact, a count.

[Hexcede]

rather the number of indices to unpack

This is incorrect. Unpack takes two indices, the second argument is not the count but rather the last index. The second argument does default to the length of the input table, but this is because the last index of the table matches the length, not because the argument is a count. This is confirmed by both the Lua 5.1 and Lua 5.4 documentation as well as through empirical testing.

[gyfdb]

rather the number of indices to unpack (default to the total number of indices)

I can see how the misunderstanding with the unpack function can be seen here. While yes, parameter j is defaulted to total number of elements in a table, it's defaulted to that because you're grabbing from start of i and ending at j. j is wherever you want unpacking to stop. table.unpack/unpack is basically like javascript's slice prototype function.

https://github.com/luau-lang/luau/blob/e76802f2ce698ca090a793b24c07e336b21ade9f/VM/src/ltablib.cpp#L269C18-L269C18
Dosen't explain much but this is the pushed global cfunction of unpack.