Acquis 16 - Slices

Slices provide a way to extract a subsequence of a sequence of values.

Usage

Subsequences can be extracted from either tables, strings, or vectors using the , operator.

local t = {1, 2, 3, 4, 5}
local s = t[2,4]  -- {2, 3, 4}

local s = "hello"
local s = s[2,4]  -- "ell"

local v = vector.create(1024)
local s = v[512,1024] -- vector from index 512 to 1024

If no starting index is provided, the slice starts from the first element:

local t = {1, 2, 3, 4, 5}
local s = t[,3]  -- {1, 2, 3}

If no ending index is provided, the slice ends at the last element:

local t = {1, 2, 3, 4, 5}
local s = t[2,]  -- {2, 3, 4, 5}

__slice

The __slice metamethod can be used to define custom slice behavior for a table.

local mt = {
    __slice = function(self, start, finish)
        start = start or 1
        finish = finish or error("Must provide finish index")
        local result = {}
        for i = start, finish do
            result[i] = i
        end
        return result
    end
}

local range = setmetatable({}, mt)
local s = range[10, 100] -- {10, 11, ... 100}
local x = range[, 100] -- {1, 2, ... 100}
assert(not catch range[100,]) -- finish index is required