Begin experimental option to not use caching.

.travis.yml

@@ -0,0 +1,39 @@
+language: erlang
+
+env:
+  global:
+    - LUAROCKS_BASE=luarocks-2.2.2
+  matrix:
+    - LUA=lua5.1 LUA_DEV=liblua5.1-dev LUA_VER=5.1 LUA_SFX=5.1 LUA_INCDIR=/usr/include/lua5.1
+    - LUA=lua5.2 LUA_DEV=liblua5.2-dev LUA_VER=5.2 LUA_SFX=5.2 LUA_INCDIR=/usr/include/lua5.2
+    - LUA=luajit LUA_DEV=libluajit-5.1-dev LUA_VER=5.1 LUA_SFX=jit LUA_INCDIR=/usr/include/luajit-2.0
+
+before_install:
+  - if [ $LUA = "luajit" ]; then
+      sudo add-apt-repository ppa:mwild1/ppa -y && sudo apt-get update -y;
+      sudo apt-get install lua5.1;
+      sudo apt-get install liblua5.1-dev;
+    fi
+  - sudo apt-get install $LUA
+  - sudo apt-get install $LUA_DEV
+  - lua$LUA_SFX -v
+  # Install a recent luarocks release
+  - wget http://luarocks.org/releases/$LUAROCKS_BASE.tar.gz
+  - tar zxvpf $LUAROCKS_BASE.tar.gz
+  - cd $LUAROCKS_BASE
+  - ./configure
+    --lua-version=$LUA_VER --lua-suffix=$LUA_SFX --with-lua-include="$LUA_INCDIR"
+  - sudo make
+  - sudo make install
+  - cd $TRAVIS_BUILD_DIR
+
+install:
+  - sudo -E luarocks install busted
+
+script:
+  - sudo -E busted -v
+
+notifications:
+  email:
+    on_success: change
+    on_failure: always

LICENSE.txt

@@ -1,4 +1,4 @@
-Copyright (c) 2015 Calvin Rose
+Copyright (c) 2016 Calvin Rose
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
 

README.md

@@ -1,5 +1,7 @@
 # tiny-ecs #
 
+[![Build Status](https://travis-ci.org/bakpakin/tiny-ecs.png?branch=master)](https://travis-ci.org/bakpakin/tiny-ecs)
+
 [![License](http://img.shields.io/badge/Licence-MIT-brightgreen.svg)](LICENSE)
 
 Tiny-ecs is an Entity Component System for lua that's simple, flexible, and useful.

rockspecs/tiny-ecs-1.2-1.rockspec

@@ -0,0 +1,24 @@
+package = "tiny-ecs"
+version = "1.2-1"
+source = {
+    url = "git://github.com/bakpakin/tiny-ecs",
+    tag = "1.2-1"
+}
+description = {
+    summary = "Entity Component System for Lua.",
+    detailed = [[
+        Pure Lua implementation of an easy to use, compact, fast, and flexible
+        Entity Component System. Works well with Object Orientation.
+    ]],
+    homepage = "https://github.com/bakpakin/tiny-ecs",
+    license = "MIT"
+}
+dependencies = {
+    "lua >= 5.1"
+}
+build = {
+    type = "builtin",
+    modules = {
+        tiny = "tiny.lua"
+    }
+}

rockspecs/tiny-ecs-1.3-1.rockspec

@@ -0,0 +1,24 @@
+package = "tiny-ecs"
+version = "1.3-1"
+source = {
+    url = "git://github.com/bakpakin/tiny-ecs",
+    tag = "1.3-1"
+}
+description = {
+    summary = "Entity Component System for Lua.",
+    detailed = [[
+        Pure Lua implementation of an easy to use, compact, fast, and flexible
+        Entity Component System. Works well with Object Orientation.
+    ]],
+    homepage = "https://github.com/bakpakin/tiny-ecs",
+    license = "MIT"
+}
+dependencies = {
+    "lua >= 5.1"
+}
+build = {
+    type = "builtin",
+    modules = {
+        tiny = "tiny.lua"
+    }
+}

spec/tiny_spec.lua

@@ -1,3 +1,8 @@
+local GLOBALS = {}
+for k, v in pairs(_G) do
+    GLOBALS[k] = v
+end
+
 local tiny = require "tiny"
 
 local function deep_copy(x)
@@ -85,6 +90,49 @@ describe('tiny-ecs:', function()
 
         end)
 
+        it("Can use functions as subfilters", function()
+
+            local f1 = tiny.requireAny('a', 'b', 'c')
+            local f2 = tiny.requireAll('x', 'y', 'z')
+            local f = tiny.requireAll(f1, f2)
+
+            assert.truthy(f(nil, {
+                x = true, y = true, z = true, a = true, b = true, c = true
+            }))
+            assert.truthy(f(nil, {
+                x = true, y = true, z = true, a = true
+            }))
+            assert.falsy(f(nil, {
+                x = true, y = true, a = true
+            }))
+            assert.falsy(f(nil, {
+                x = true, y = true, z = true
+            }))
+
+        end)
+
+        it("Can use string filters", function()
+
+            local f = tiny.filter('a|b|c')
+
+            assert.truthy(f(nil, {
+                a = true, b = true, c = true
+            }))
+            assert.truthy(f(nil, {
+                a = true
+            }))
+            assert.truthy(f(nil, {
+                b = true
+            }))
+            assert.truthy(f(nil, {
+                c = true
+            }))
+            assert.falsy(f(nil, {
+                x = true, y = true, z = true
+            }))
+
+        end)
+
     end)
 
     describe('World:', function()
@@ -115,6 +163,11 @@ describe('tiny-ecs:', function()
             timePassed = 0
         end)
 
+        after_each(function()
+            world:clearSystems()
+            world:refresh()
+        end)
+
         it("Create World", function()
             assert.equals(world:getEntityCount(), 3)
             assert.equals(world:getSystemCount(), 2)
@@ -180,9 +233,11 @@ describe('tiny-ecs:', function()
         end)
 
         it("Remove Entities Multiple Times", function()
+            assert.equals(3, world:getEntityCount())
             world:update(1)
             world:remove(entity1, entity2, entity3)
             world:update(2)
+            assert.equals(0, world:getEntityCount())
             world:remove(entity1, entity2, entity3)
             world:update(2)
             assert.equals(2, world:getSystemCount())
@@ -191,7 +246,7 @@ describe('tiny-ecs:', function()
 
         it("Add Systems Multiple Times", function()
             world:update(1)
-            world:add(moveSystem, oneTimeSystem)
+            assert.has_error(function() world:add(moveSystem, oneTimeSystem) end, "System already belongs to a World.")
             world:update(2)
             assert.equals(2, world:getSystemCount())
             assert.equals(3, world:getEntityCount())
@@ -201,7 +256,7 @@ describe('tiny-ecs:', function()
             world:update(1)
             world:remove(moveSystem)
             world:update(2)
-            world:remove(moveSystem)
+            assert.has_error(function() world:remove(moveSystem) end, "System does not belong to this World.")
             world:update(2)
             assert.equals(1, world:getSystemCount())
             assert.equals(3, world:getEntityCount())
@@ -217,12 +272,12 @@ describe('tiny-ecs:', function()
 
         it("Sorts Entities in Sorting Systems", function()
             local sortsys = tiny.sortedProcessingSystem()
-            sortsys.filter = tiny.requireAll("vel")
+            sortsys.filter = tiny.filter("vel|xform")
             function sortsys:compare(e1, e2)
                 return e1.vel.x < e2.vel.x
             end
             world:add(sortsys)
-            world:update(0)
+            world:refresh()
             assert.equals(sortsys.entities[1], entity2)
             assert.equals(sortsys.entities[2], entity3)
             assert.equals(sortsys.entities[3], entity1)
@@ -230,4 +285,8 @@ describe('tiny-ecs:', function()
 
     end)
 
+    it("Doesn't pollute the global namespace", function()
+        assert.are.same(_G, GLOBALS)
+    end)
+
 end)

tiny.lua

@@ -1,5 +1,5 @@
 --[[
-Copyright (c) 2015 Calvin Rose
+Copyright (c) 2016 Calvin Rose
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of
 this software and associated documentation files (the "Software"), to deal in
@@ -23,13 +23,12 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 -- @author Calvin Rose
 -- @license MIT
 -- @copyright 2015
-local tiny = { _VERSION = "1.1-7" }
+local tiny = { _VERSION = "scm" }
 
 -- Local versions of standard lua functions
 local tinsert = table.insert
 local tremove = table.remove
 local tsort = table.sort
-local pairs = pairs
 local setmetatable = setmetatable
 local type = type
 local select = select
@@ -85,88 +84,121 @@ local tiny_remove
 --
 -- @section Filter
 
+-- A helper function to compile filters.
+local filterJoin
+
+-- A helper function to filters from string
+local filterBuildString
+
+do
+
+    local loadstring = loadstring or load
+    local function getchr(c)
+        return "\\" .. c:byte()
+    end
+    local function make_safe(text)
+        return ("%q"):format(text):gsub('\n', 'n'):gsub("[\128-\255]", getchr)
+    end
+
+    local function filterJoinRaw(prefix, seperator, ...)
+        local accum = {}
+        local build = {}
+        for i = 1, select('#', ...) do
+            local item = select(i, ...)
+            if type(item) == 'string' then
+                accum[#accum + 1] = ("(e[%s] ~= nil)"):format(make_safe(item))
+            elseif type(item) == 'function' then
+                build[#build + 1] = ('local subfilter_%d_ = select(%d, ...)'):format(i, i)
+                accum[#accum + 1] = ('(subfilter_%d_(system, e))'):format(i)
+            else
+                error 'Filter token must be a string or a filter function.'
+            end
+        end
+        local source = ('do %s\n return function(system, e) return %s(%s) end end'):format(
+            table.concat(build, '\n'),
+            prefix,
+            table.concat(accum, seperator)
+        )
+        local loader, err = loadstring(source)
+        if err then error(err) end
+        return loader(...)
+    end
+
+    function filterJoin(...)
+        local state, value = pcall(filterJoinRaw, ...)
+        if state then return value else return nil, value end
+    end
+
+    local function buildPart(str)
+        local accum = {}
+        local subParts = {}
+        str = str:gsub('%b()', function(p)
+            subParts[#subParts + 1] = buildPart(p:sub(2, -2))
+            return ('\255%d'):format(#subParts)
+        end)
+        for invert, part, sep in str:gmatch('(%!?)([^%|%&%!]+)([%|%&%!]?)') do
+            if part:match('^\255%d+$') then
+                local partIndex = tonumber(part:match(part:sub(2)))
+                accum[#accum + 1] = ('%s(%s)'):format(invert == '' and '' or 'not', subParts[partIndex])
+            else
+                accum[#accum + 1] = ("(e[%s] %s nil)"):format(make_safe(part), invert == '' and '~=' or '==')
+            end
+            if sep ~= '' then
+                accum[#accum + 1] = (sep == '|' and ' or ' or ' and ')
+            end
+        end
+        return table.concat(accum)
+    end
+
+    function filterBuildString(str)
+        local source = ("return function(_, e) return %s end"):format(buildPart(str))
+        local loader, err = loadstring(source)
+        if err then
+            error(err)
+        end
+        return loader()
+    end
+
+end
+
 --- Makes a Filter that selects Entities with all specified Components and
 -- Filters.
 function tiny.requireAll(...)
-    local components = {...}
-    local len = #components
-    return function(system, e)
-        local c
-        for i = 1, len do
-            c = components[i]
-            if type(c) == 'function' then
-                if not c(system, e) then
-                    return false
-                end
-            elseif e[c] == nil then
-                return false
-            end
-        end
-        return true
-    end
+    return filterJoin('', ' and ', ...)
 end
 
 --- Makes a Filter that selects Entities with at least one of the specified
 -- Components and Filters.
 function tiny.requireAny(...)
-    local components = {...}
-    local len = #components
-    return function(system, e)
-        local c
-        for i = 1, len do
-            c = components[i]
-            if type(c) == 'function' then
-                if c(system, e) then
-                    return true
-                end
-            elseif e[c] ~= nil then
-                return true
-            end
-        end
-        return false
-    end
+    return filterJoin('', ' or ', ...)
 end
 
 --- Makes a Filter that rejects Entities with all specified Components and
 -- Filters, and selects all other Entities.
 function tiny.rejectAll(...)
-    local components = {...}
-    local len = #components
-    return function(system, e)
-        local c
-        for i = 1, len do
-            c = components[i]
-            if type(c) == 'function' then
-                if not c(system, e) then
-                    return true
-                end
-            elseif e[c] == nil then
-                return true
-            end
-        end
-        return false
-    end
+    return filterJoin('not', ' and ', ...)
 end
 
 --- Makes a Filter that rejects Entities with at least one of the specified
 -- Components and Filters, and selects all other Entities.
 function tiny.rejectAny(...)
-    local components = {...}
-    local len = #components
-    return function(system, e)
-        local c
-        for i = 1, len do
-            c = components[i]
-            if type(c) == 'function' then
-                if c(system, e) then
-                    return false
-                end
-            elseif e[c] ~= nil then
-                return false
-            end
-        end
-        return true
+    return filterJoin('not', ' or ', ...)
 end
+
+--- Makes a Filter from a string. Syntax of `pattern` is as follows.
+--
+--   * Tokens are alphanumeric strings including underscores.
+--   * Tokens can be separated by |, &, or surrounded by parentheses.
+--   * Tokens can be prefixed with !, and are then operated on with a boolean 'not'.
+--
+-- Examples are best:
+--    'a|b|c' - Matches entities with an 'a' component OR a 'b' component or a 'c' component.
+--    'a&!b&c' - Matches entities with an 'a' component AND NOT a 'b' component AND a 'c' component.
+--    'a|(b&c&d)|e - Matches 'a' OR ('b' AND 'c' AND 'd') OR 'e'
+-- @param pattern
+function tiny.filter(pattern)
+    local state, value = pcall(filterBuildString, pattern)
+    if state then return value else return nil, value end
 end
 
 --- System functions.
@@ -187,6 +219,10 @@ end
 -- from the System.
 --   * `function system:onModify(dt)` - Called when the System is modified by
 -- adding or removing Entities from the System.
+--   * `function system:onAddToWorld(world)` - Called when the System is added
+-- to the World, before any entities are added to the system.
+--   * `function system:onRemoveFromWorld(world)` - Called when the System is
+-- removed from the world, after all Entities are removed from the System.
 --
 -- For Filters, it is convenient to use `tiny.requireAll` or `tiny.requireAny`,
 -- but one can write their own filters as well. Set the Filter of a System like
@@ -235,30 +271,40 @@ end
 
 -- Update function for all Processing Systems.
 local function processingSystemUpdate(system, dt)
-    local entities = system.entities
     local preProcess = system.preProcess
     local process = system.process
     local postProcess = system.postProcess
-    local entity
 
     if preProcess then
         preProcess(system, dt)
     end
 
     if process then
-        local len = #entities
-        for i = 1, len do
-            entity = entities[i]
+        if system.nocache then
+            local entities = system.world.entityList
+            local filter = system.filter
+            if filter then
+                for i = 1, #entities do
+                    local entity = entities[i]
+                    if filter(system, entity) then
                         process(system, entity, dt)
                     end
                 end
+            end
+        else
+            local entities = system.entities
+            for i = 1, #entities do
+                process(system, entities[i], dt)
+            end
+        end
+    end
 
     if postProcess then
         postProcess(system, dt)
     end
 end
 
--- Sorts Systems by a function system.sort(entity1, entity2) on modify.
+-- Sorts Systems by a function system.sortDelegate(entity1, entity2) on modify.
 local function sortedSystemOnModify(system, dt)
     local entities = system.entities
     local indices = system.indices
@@ -272,8 +318,7 @@ local function sortedSystemOnModify(system, dt)
     end
     tsort(entities, sortDelegate)
     for i = 1, #entities do
-        local entity = entities[i]
-        indices[entity] = i
+        indices[entities[i]] = i
     end
 end
 
@@ -290,9 +335,9 @@ end
 -- Processing Systems have three extra callbacks besides those inheritted from
 -- vanilla Systems.
 --
---     function system:preProcess(entities, dt) -- Called before iteration.
---     function system:process(entities, dt) -- Process each entity.
---     function system:postProcess(entity, dt) -- Called after iteration.
+--     function system:preProcess(dt) -- Called before iteration.
+--     function system:process(entity, dt) -- Process each entity.
+--     function system:postProcess(dt) -- Called after iteration.
 --
 -- Processing Systems have their own `update` method, so don't implement a
 -- a custom `update` callback for Processing Systems.
@@ -348,7 +393,7 @@ local worldMetaTable
 -- Can optionally add default Systems and Entities. Returns the new World along
 -- with default Entities and Systems.
 function tiny.world(...)
-    local ret = {
+    local ret = setmetatable({
 
         -- List of Entities to add
         entitiesToAdd = {},
@@ -356,6 +401,9 @@ function tiny.world(...)
         -- List of Entities to remove
         entitiesToRemove = {},
 
+        -- List of Entities to change
+        entitiesToChange = {},
+
         -- List of Entities to add
         systemsToAdd = {},
 
@@ -365,28 +413,33 @@ function tiny.world(...)
         -- Set of Entities
         entities = {},
 
+        -- List of Entities
+        entityList = {},
+
         -- Number of Entities in World
         entityCount = 0,
 
         -- List of Systems
         systems = {}
-    }
+    }, worldMetaTable)
 
     tiny_add(ret, ...)
     tiny_manageSystems(ret)
     tiny_manageEntities(ret)
 
-    return setmetatable(ret, worldMetaTable), ...
+    return ret, ...
 end
 
 --- Adds an Entity to the world.
 -- Also call this on Entities that have changed Components such that they
 -- match different Filters. Returns the Entity.
 function tiny.addEntity(world, entity)
+    if world.entities[entity] then
+        local e2c = world.entitiesToChange
+        e2c[#e2c + 1] = entity
+    else
         local e2a = world.entitiesToAdd
         e2a[#e2a + 1] = entity
-    if world.entities[entity] then
-        tiny_removeEntity(world, entity)
     end
     return entity
 end
@@ -394,8 +447,10 @@ tiny_addEntity = tiny.addEntity
 
 --- Adds a System to the world. Returns the System.
 function tiny.addSystem(world, system)
+    assert(system.world == nil, "System already belongs to a World.")
     local s2a = world.systemsToAdd
     s2a[#s2a + 1] = system
+    system.world = world
     return system
 end
 tiny_addSystem = tiny.addSystem
@@ -403,9 +458,8 @@ tiny_addSystem = tiny.addSystem
 --- Shortcut for adding multiple Entities and Systems to the World. Returns all
 -- added Entities and Systems.
 function tiny.add(world, ...)
-    local obj
     for i = 1, select("#", ...) do
-        obj = select(i, ...)
+        local obj = select(i, ...)
         if obj then
             if isSystem(obj) then
                 tiny_addSystem(world, obj)
@@ -428,6 +482,7 @@ tiny_removeEntity = tiny.removeEntity
 
 --- Removes a System from the world. Returns the System.
 function tiny.removeSystem(world, system)
+    assert(system.world == world, "System does not belong to this World.")
     local s2r = world.systemsToRemove
     s2r[#s2r + 1] = system
     return system
@@ -437,9 +492,8 @@ tiny_removeSystem = tiny.removeSystem
 --- Shortcut for removing multiple Entities and Systems from the World. Returns
 -- all removed Systems and Entities
 function tiny.remove(world, ...)
-    local obj
     for i = 1, select("#", ...) do
-        obj = select(i, ...)
+        local obj = select(i, ...)
         if obj then
             if isSystem(obj) then
                 tiny_removeSystem(world, obj)
@@ -461,19 +515,19 @@ function tiny_manageSystems(world)
         return
     end
 
-        local entities = world.entities
+    world.systemsToAdd = {}
+    world.systemsToRemove = {}
+
+    local worldEntityList = world.entityList
     local systems = world.systems
-        local system, index, filter
-        local entityList, entityIndices, entityIndex, onRemove, onAdd
 
     -- Remove Systems
     for i = 1, #s2r do
-            system = s2r[i]
-            index = system.index
-            if system.world == world then
-                onRemove = system.onRemove
-                if onRemove then
-                    entityList = system.entities
+        local system = s2r[i]
+        local index = system.index
+        local onRemove = system.onRemove
+        if onRemove and not system.nocache then
+            local entityList = system.entities
             for j = 1, #entityList do
                 onRemove(system, entityList[j])
             end
@@ -482,6 +536,9 @@ function tiny_manageSystems(world)
         for j = index, #systems do
             systems[j].index = j
         end
+        local onRemoveFromWorld = system.onRemoveFromWorld
+        if onRemoveFromWorld then
+            onRemoveFromWorld(system, world)
         end
         s2r[i] = nil
 
@@ -494,28 +551,36 @@ function tiny_manageSystems(world)
 
     -- Add Systems
     for i = 1, #s2a do
-            system = s2a[i]
-            if systems[system.index] ~= system then
-                entityList = {}
-                entityIndices = {}
-                system.entities = entityList
-                system.indices = entityIndices
+        local system = s2a[i]
+        if systems[system.index or 0] ~= system then
+            if not system.nocache then
+                system.entities = {}
+                system.indices = {}
+            end
             if system.active == nil then
                 system.active = true
             end
             system.modified = true
             system.world = world
-                index = #systems + 1
+            local index = #systems + 1
             system.index = index
             systems[index] = system
+            local onAddToWorld = system.onAddToWorld
+            if onAddToWorld then
+                onAddToWorld(system, world)
+            end
 
             -- Try to add Entities
-                onAdd = system.onAdd
-                filter = system.filter
+            if not system.nocache then
+                local entityList = system.entities
+                local entityIndices = system.indices
+                local onAdd = system.onAdd
+                local filter = system.filter
                 if filter then
-                    for entity in pairs(entities) do
+                    for j = 1, #worldEntityList do
+                        local entity = worldEntityList[j]
                         if filter(system, entity) then
-                            entityIndex = #entityList + 1
+                            local entityIndex = #entityList + 1
                             entityList[entityIndex] = entity
                             entityIndices[entity] = entityIndex
                             if onAdd then
@@ -525,82 +590,135 @@ function tiny_manageSystems(world)
                     end
                 end
             end
+        end
         s2a[i] = nil
     end
 end
 
--- Adds and removes Entities that have been marked.
+-- Adds, removes, and changes Entities that have been marked.
 function tiny_manageEntities(world)
-    local e2a, e2r = world.entitiesToAdd, world.entitiesToRemove
+
+    local e2a = world.entitiesToAdd
+    local e2r = world.entitiesToRemove
+    local e2c = world.entitiesToChange
 
     -- Early exit
-    if #e2a == 0 and #e2r == 0 then
+    if #e2a == 0 and #e2r == 0 and #e2c == 0 then
         return
     end
 
+    world.entitiesToChange = {}
+    world.entitiesToAdd = {}
+    world.entitiesToRemove = {}
+
     local entities = world.entities
+    local entityList = world.entityList
     local systems = world.systems
     local entityCount = world.entityCount
-    local entity, system, index
-    local onRemove, onAdd, ses, seis, filter, tmpEntity
 
-    -- Remove Entities
-    for i = 1, #e2r do
-        entity = e2r[i]
+    -- Change Entities
+    for i = 1, #e2c do
+        local entity = e2c[i]
         if entities[entity] then
-            entities[entity] = nil
-            entityCount = entityCount - 1
-
             for j = 1, #systems do
-                system = systems[j]
-                ses = system.entities
-                seis = system.indices
-                index = seis[entity]
-
-                if index then
-                    system.modified = true
-                    tmpEntity = ses[#ses]
-                    ses[index] = tmpEntity
-                    seis[tmpEntity] = index
-                    seis[entity] = nil
-                    ses[#ses] = nil
-                    onRemove = system.onRemove
-                    if onRemove then
-                        onRemove(system, entity)
-                    end
-                end
-
-            end
-
-        end
-        e2r[i] = nil
-    end
-
-    -- Add Entities
-    for i = 1, #e2a do
-        entity = e2a[i]
-        if not entities[entity] then
-            entities[entity] = true
-            entityCount = entityCount + 1
-
-            for j = 1, #systems do
-                system = systems[j]
-                ses = system.entities
-                seis = system.indices
-                filter = system.filter
+                local system = systems[j]
+                if not system.nocache then
+                    local ses = system.entities
+                    local seis = system.indices
+                    local index = seis[entity]
+                    local filter = system.filter
                     if filter and filter(system, entity) then
+                        if not index then
                             system.modified = true
                             index = #ses + 1
                             ses[index] = entity
                             seis[entity] = index
-                    onAdd = system.onAdd
+                            local onAdd = system.onAdd
                             if onAdd then
                                 onAdd(system, entity)
                             end
                         end
-
+                    elseif index then
+                        system.modified = true
+                        local tmpEntity = ses[#ses]
+                        ses[index] = tmpEntity
+                        seis[tmpEntity] = index
+                        seis[entity] = nil
+                        ses[#ses] = nil
+                        local onRemove = system.onRemove
+                        if onRemove then
+                            onRemove(system, entity)
+                        end
+                    end
+                end
+            end
+        end
+        e2c[i] = nil
     end
 
+    -- Remove Entities
+    for i = 1, #e2r do
+        local entity = e2r[i]
+        e2r[i] = nil
+        local listIndex = entities[entity]
+        if listIndex then
+            -- Remove Entity from world state
+            local lastEntity = entityList[#entityList]
+            entities[lastEntity] = listIndex
+            entities[entity] = nil
+            entityList[listIndex] = lastEntity
+            entityList[#entityList] = nil
+            entityCount = entityCount - 1
+            -- Remove from cached systems
+            for j = 1, #systems do
+                local system = systems[j]
+                if not system.nocache then
+                    local ses = system.entities
+                    local seis = system.indices
+                    local index = seis[entity]
+                    if index then
+                        system.modified = true
+                        local tmpEntity = ses[#ses]
+                        ses[index] = tmpEntity
+                        seis[tmpEntity] = index
+                        seis[entity] = nil
+                        ses[#ses] = nil
+                        local onRemove = system.onRemove
+                        if onRemove then
+                            onRemove(system, entity)
+                        end
+                    end
+                end
+            end
+        end
+    end
+
+    -- Add Entities
+    for i = 1, #e2a do
+        local entity = e2a[i]
+        if not entities[entity] then
+            local listIndex = #entityList + 1
+            entities[entity] = listIndex
+            entityList[listIndex] = entity
+            entityCount = entityCount + 1
+            for j = 1, #systems do
+                local system = systems[j]
+                if not system.nocache then
+                    local ses = system.entities
+                    local seis = system.indices
+                    local filter = system.filter
+                    if filter and filter(system, entity) then
+                        system.modified = true
+                        local index = #ses + 1
+                        ses[index] = entity
+                        seis[entity] = index
+                        local onAdd = system.onAdd
+                        if onAdd then
+                            onAdd(system, entity)
+                        end
+                    end
+                end
+            end
         end
         e2a[i] = nil
     end
@@ -615,6 +733,17 @@ end
 function tiny.refresh(world)
     tiny_manageSystems(world)
     tiny_manageEntities(world)
+    local systems = world.systems
+    for i = 1, #systems do
+        local system = systems[i]
+        if system.active then
+            local onModify = system.onModify
+            if onModify and system.modified then
+                onModify(system, 0)
+            end
+            system.modified = false
+        end
+    end
 end
 
 --- Updates the World by dt (delta time). Takes an optional parameter, `filter`,
@@ -627,23 +756,22 @@ function tiny.update(world, dt, filter)
     tiny_manageEntities(world)
 
     local systems = world.systems
-    local system, update, interval, onModify
 
     --  Iterate through Systems IN ORDER
     for i = 1, #systems do
-        system = systems[i]
+        local system = systems[i]
         if system.active and ((not filter) or filter(world, system)) then
 
             -- Call the modify callback on Systems that have been modified.
-            onModify = system.onModify
+            local onModify = system.onModify
             if onModify and system.modified then
                 onModify(system, dt)
             end
 
             -- Update Systems that have an update method (most Systems)
-            update = system.update
+            local update = system.update
             if update then
-                interval = system.interval
+                local interval = system.interval
                 if interval then
                     local bufferedTime = (system.bufferedTime or 0) + dt
                     while bufferedTime >= interval do
@@ -665,8 +793,9 @@ end
 
 --- Removes all Entities from the World.
 function tiny.clearEntities(world)
-    for e in pairs(world.entities) do
-        tiny_removeEntity(world, e)
+    local el = world.entityList
+    for i = 1, #el do
+        tiny_removeEntity(world, el[i])
     end
 end
 
@@ -701,6 +830,10 @@ function tiny.setSystemIndex(world, system, index)
     local oldIndex = system.index
     local systems = world.systems
 
+    if index < 0 then
+        index = tiny.getSystemCount(world) + 1 + index
+    end
+
     tremove(systems, oldIndex)
     tinsert(systems, index, system)
 
@@ -728,7 +861,10 @@ worldMetaTable = {
         getSystemCount = tiny.getSystemCount,
         getSystemIndex = tiny.getSystemIndex,
         setSystemIndex = tiny.setSystemIndex
-    }
+    },
+    __tostring = function(self)
+        return "<tiny-ecs_World>"
+    end
 }
 
 return tiny