Iterator
An iterator is a design pattern that allows you to go through all the items in a collection (like a list, stack, or tree) one by one, without needing to know how the collection is built or stored.
One of the main data structures in the Lua programming language is a table. Lua already has a built-in iterator for tables next, read a post about iterators in Lua. To keep the consistency of the design patterns series, here we will make a simple class implementation of the iterator.
TableIterator class and usage
---@class TableIterator
---@field private collection table
---@field private index number
local TableIterator = {}
TableIterator.__index = TableIterator
---@return TableIterator
---@param collection table
function TableIterator:new(collection)
local t = {
index = 1,
collection = collection,
}
return setmetatable(t, self)
end
function TableIterator:next()
local element = self.collection[self.index]
if not element then
return nil
end
self.index = self.index + 1
return element
end
local t = { "Hello", "World", "of", "Iterators" }
local iterator = TableIterator:new(t)
local element = iterator:next()
while element do
print(element)
element = iterator:next()
end
--[[
Hello
World
of
Iterators
--]]
Without class
Class is really overhead for this simple example and can be replaced with a simple function.
---@param collection table
---@return function
function createTableIterator(collection)
local index = 1
return function()
local element = collection[index]
if not element then
return nil
end
index = index + 1
return element
end
end
local tableNext = createTableIterator(t)
local element = tableNext()
while element do
print(element)
element = tableNext()
end
--[[
Hello
World
of
Iterators
--]]