Item - a utility helper for Lua Tables (based on Laravel Collections)

item.lua

-- Lua Table utility helper
-- Inspired by: https://laravel.com/docs/8.x/collections

Item = {}
Item.__index = Item

-- initializer
function Item:create(items)
	assert(type(items) == 'table', 'Item expects a table.')
  
	self.__index = self
  
	return setmetatable({ items = items }, Item)
end

-- pretty print
function Item:__tostring()
    local out = {}
  
	for k, v in pairs(self.items) do
		table.insert(out, string.format('%s=%s', k, v))
	end
  
	return '{ ' .. table.concat(out, ', ') .. ' }'
end

-- iterates through each item, sending it's
-- key and value through the given callback
function Item:map(cb)
	for k, v in pairs(self.items) do
		self.items[k] = cb(v, k)
	end
  
	return self
end

-- iterates though each item, filters out
-- non-truthy values returned by given callback
function Item:filter(cb)
	for k, v in pairs(self.items) do
  	if not cb(v, k) then
    	self.items[k] = nil
    end
  end
	
	return self
end

-- iterates though each item, filters out
-- truthy values returned by given callback
function Item:reject(cb)
	for k, v in pairs(self.items) do
  	if cb(v, k) then
    	self.items[k] = nil
    end
  end
	
	return self
end

-- merge new tbl into original table,
-- overriding existing values
function Item:merge(tbl)
  if type(tbl) == 'table' then
    for k, v in pairs(tbl) do
      self.items[k] = v
    end
  end
  
	return self
end

return Item

usage.lua

-- Usage example of Item class
--
local Item = require 'item'

-- helper function
function items(...)
	return Item:create(...)
end

-- input
local tbl1 = { a = 1, b = 2, c = 3, d = 4, e = 5 }
local tbl2 -- updated

-- map, doubles every value
tbl2 = items(tbl):map(function(v, k)
	return v * 2
end)

-- output
print(tbl2) -- { a=2, b=4, c=6, d=8, e=10 }