Merge pull request #25 from yangruihan/master

fix README.md example error

.travis.yml

@@ -1,8 +1,8 @@
-language: erlang
+language: c
 
 env:
   global:
-    - LUAROCKS_BASE=luarocks-2.2.2
+    - LUAROCKS_BASE=luarocks-3.2.1
   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

README.md

@@ -1,29 +1,34 @@
 # tiny-ecs #
 
-[![Build Status](https://travis-ci.org/bakpakin/tiny-ecs.png?branch=master)](https://travis-ci.org/bakpakin/tiny-ecs)
+## NOTE
 
-[![License](http://img.shields.io/badge/Licence-MIT-brightgreen.svg)](LICENSE)
+Although there have been almost no commits in several years, this
+project is not abandoned. tiny-ecs is, for most intents and
+purposes, finished, and no bugs have been brought to my attention in a while.
+New issues on GitHub will be addressed.
 
-Tiny-ecs is an Entity Component System for lua that's simple, flexible, and useful.
+[![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)
-Because of lua's tabular nature, Entity Component Systems are a natural choice
+
+Tiny-ecs is an Entity Component System for Lua that's simple, flexible, and useful.
+Because of Lua's tabular nature, Entity Component Systems are a natural choice
 for simulating large and complex systems. For more explanation on Entity
 Component Systems, here is some
 [basic info](http://en.wikipedia.org/wiki/Entity_component_system "Wikipedia").
 
-Tiny-ecs also works well with objected oriented programming in lua because
+Tiny-ecs also works well with object-oriented programming in Lua because
 Systems and Entities do not use metatables. This means you can subclass your
-Systems and Entities, and use existing lua class frameworks with tiny-ecs, no problem.
+Systems and Entities and use existing Lua class frameworks with tiny-ecs, no problem.
-For an example on how to use tiny-ecs with object-oriented lua, take a look at the
+For an example on how to use tiny-ecs with object-oriented Lua, take a look at the
-demo branch, specifically the systems and entities sub-directories.
+demo branch, specifically the systems and entities subdirectories.
 
 ## Overview ##
 Tiny-ecs has four important types: Worlds, Filters, Systems, and Entities.
-Entities, however, can be any lua table, and Filters are just functions that
+Entities, however, can be any Lua table, and Filters are just functions that
 take an Entity as a parameter.
 
 ### Entities ###
-Entities are simply lua tables of data that gets processed by Systems. Entities
+Entities are simply Lua tables of data that gets processed by Systems. Entities
-should contain primarily data rather than code, as it is the Systems's job to
+should contain primarily data rather than code, as it is the System's job to
 do logic on data. Henceforth, a key-value pair in an Entity will
 be referred to as a Component.
 
@@ -39,7 +44,7 @@ provides functions for creating Systems easily, as well as creating Systems that
 can be used in an object oriented fashion.
 
 ### Filters ###
-Filters are used to select Entities. Filters can be any lua function, but
+Filters are used to select Entities. Filters can be any Lua function, but
 tiny-ecs provides some functions for generating common ones, like selecting
 only Entities that have all required components.
 
@@ -51,7 +56,7 @@ local talkingSystem = tiny.processingSystem()
 talkingSystem.filter = tiny.requireAll("name", "mass", "phrase")
 function talkingSystem:process(e, dt)
     e.mass = e.mass + dt * 3
-    print(e.name .. ", who weighs " .. e.mass .. " pounds, says, \"" .. e.phrase .. "\"")
+    print(("%s who weighs %d pounds, says %q."):format(e.name, e.mass, e.phrase))
 end
 
 local joe = {
@@ -70,17 +75,16 @@ end
 
 ## Use It ##
 Copy paste tiny.lua into your source folder. For stability and consistent API,
-please use a tagged release or use luarocks. Tagged releases will have a version
+please use a tagged release or use LuaRocks.
-number in `tiny._VERSION`, while other commits will just have the string 'scm'.
 
 ## Luarocks ##
-Tiny-ecs is also on [Luarocks](https://luarocks.org/) and can be installed with
+Tiny-ecs is also on [LuaRocks](https://luarocks.org/) and can be installed with
 `luarocks install tiny-ecs`.
 
 ## Demo ##
 Check out the [demo](https://github.com/bakpakin/tiny-ecs/tree/demo-commandokibbles), a game
 originally written for Ludum Dare 32 with the theme 'An Unconventional Weapon'. The demo uses
-[LÖVE](https://love2d.org/), an amazing game framework for lua.
+[LÖVE](https://love2d.org/), an amazing game framework for Lua.
 
 ## Testing ##
 Tiny-ecs uses [busted](http://olivinelabs.com/busted/) for testing. Install and run

config.ld

@@ -5,7 +5,7 @@ backtick_references = true
 format = 'discount'
 title = "tiny-ecs API"
 one = true
-dir = doc
+dir = "doc"
 style = '!fixed'
 package = 'tiny-ecs'
 not_luadoc = true

init.lua

@@ -0,0 +1,6 @@
+-- Helper Lua file for easy require if tiny-ecs is used as a git submodule or
+-- folder. Not needed in many cases, including luarocks distribution.
+
+local args = {...}
+local directory = args[1]
+return require(directory .. '.tiny')

rockspecs/tiny-ecs-1.0-2.rockspec

@@ -2,7 +2,7 @@ package = "tiny-ecs"
 version = "1.0-2"
 source = {
     url = "git://github.com/bakpakin/tiny-ecs",
-    tag = "1.0-2"
+    tag = version
 }
 description = {
     summary = "Entity Component System for Lua.",

rockspecs/tiny-ecs-1.1-1.rockspec

@@ -2,7 +2,7 @@ package = "tiny-ecs"
 version = "1.1-1"
 source = {
     url = "git://github.com/bakpakin/tiny-ecs",
-    tag = "1.1-1"
+    tag = version
 }
 description = {
     summary = "Entity Component System for Lua.",

rockspecs/tiny-ecs-1.1-2.rockspec

@@ -2,7 +2,7 @@ package = "tiny-ecs"
 version = "1.1-2"
 source = {
     url = "git://github.com/bakpakin/tiny-ecs",
-    tag = "1.1-2"
+    tag = version
 }
 description = {
     summary = "Entity Component System for Lua.",

rockspecs/tiny-ecs-1.1-3.rockspec

@@ -2,7 +2,7 @@ package = "tiny-ecs"
 version = "1.1-3"
 source = {
     url = "git://github.com/bakpakin/tiny-ecs",
-    tag = "1.1-3"
+    tag = version
 }
 description = {
     summary = "Entity Component System for Lua.",

rockspecs/tiny-ecs-1.1-4.rockspec

@@ -2,7 +2,7 @@ package = "tiny-ecs"
 version = "1.1-4"
 source = {
     url = "git://github.com/bakpakin/tiny-ecs",
-    tag = "1.1-4"
+    tag = version
 }
 description = {
     summary = "Entity Component System for Lua.",

rockspecs/tiny-ecs-1.1-5.rockspec

@@ -2,7 +2,7 @@ package = "tiny-ecs"
 version = "1.1-5"
 source = {
     url = "git://github.com/bakpakin/tiny-ecs",
-    tag = "1.1-5"
+    tag = version
 }
 description = {
     summary = "Entity Component System for Lua.",

rockspecs/tiny-ecs-1.1-6.rockspec

@@ -2,7 +2,7 @@ package = "tiny-ecs"
 version = "1.1-6"
 source = {
     url = "git://github.com/bakpakin/tiny-ecs",
-    tag = "1.1-6"
+    tag = version
 }
 description = {
     summary = "Entity Component System for Lua.",

rockspecs/tiny-ecs-1.1-7.rockspec

@@ -2,7 +2,7 @@ package = "tiny-ecs"
 version = "1.1-7"
 source = {
     url = "git://github.com/bakpakin/tiny-ecs",
-    tag = "1.1-7"
+    tag = version
 }
 description = {
     summary = "Entity Component System for Lua.",

rockspecs/tiny-ecs-1.2-1.rockspec

@@ -2,7 +2,7 @@ package = "tiny-ecs"
 version = "1.2-1"
 source = {
     url = "git://github.com/bakpakin/tiny-ecs",
-    tag = "1.2-1"
+    tag = version
 }
 description = {
     summary = "Entity Component System for Lua.",

rockspecs/tiny-ecs-1.3-1.rockspec

@@ -2,7 +2,7 @@ package = "tiny-ecs"
 version = "1.3-1"
 source = {
     url = "git://github.com/bakpakin/tiny-ecs",
-    tag = "1.3-1"
+    tag = version
 }
 description = {
     summary = "Entity Component System for Lua.",

rockspecs/tiny-ecs-1.3-2.rockspec

@@ -0,0 +1,24 @@
+package = "tiny-ecs"
+version = "1.3-2"
+source = {
+   url = "git://github.com/bakpakin/tiny-ecs",
+   tag = version
+}
+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-1.3-3.rockspec

@@ -0,0 +1,24 @@
+package = "tiny-ecs"
+version = "1.3-3"
+source = {
+   url = "git://github.com/bakpakin/tiny-ecs",
+   tag = version
+}
+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

@@ -233,9 +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())
@@ -270,21 +272,52 @@ 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)
         end)
 
+        it("Runs preWrap and postWrap for systems.", function()
+            local str = ""
+            local sys1 = tiny.system()
+            local sys2 = tiny.system()
+            function sys1:preWrap(dt)
+                str = str .. "<"
+            end
+            function sys2:preWrap(dt)
+                str = str .. "{"
+            end
+            function sys1:postWrap(dt)
+                str = str .. ">"
+            end
+            function sys2:postWrap(dt)
+                str = str .. "}"
+            end
+            world:add(sys1, sys2)
+            world:update(1)
+            assert.equals(str, "{<>}")
+        end)
+
     end)
 
     it("Doesn't pollute the global namespace", function()
         assert.are.same(_G, GLOBALS)
     end)
 
+    it("Can set system indices", function()
+        local world = tiny.world()
+        local systemA = tiny.system()
+        local systemB = tiny.system()
+        world:addSystem(systemA)
+        world:addSystem(systemB)
+        world:setSystemIndex(systemA, 1)
+        assert(true)
+    end)
+
 end)

test.lua

@@ -0,0 +1,8 @@
+local tiny = require('tiny')
+
+local world = tiny.world()
+local systemA = tiny.system()
+local systemB = tiny.system()
+world:addSystem(systemA)
+world:addSystem(systemB)
+world:setSystemIndex(systemA, 1)

tiny.lua

@@ -22,14 +22,13 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 --- @module tiny-ecs
 -- @author Calvin Rose
 -- @license MIT
--- @copyright 2015
+-- @copyright 2016
-local tiny = { _VERSION = "1.3-1" }
+local tiny = {}
 
 -- 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
@@ -42,12 +41,13 @@ local tiny_addSystem
 local tiny_add
 local tiny_removeEntity
 local tiny_removeSystem
-local tiny_remove
 
 --- Filter functions.
 -- A Filter is a function that selects which Entities apply to a System.
 -- Filters take two parameters, the System and the Entity, and return a boolean
--- value indicating if the Entity should be processed by the System.
+-- value indicating if the Entity should be processed by the System. A truthy
+-- value includes the entity, while a falsey (nil or false) value excludes the
+-- entity.
 --
 -- Filters must be added to Systems by setting the `filter` field of the System.
 -- Filter's returned by tiny-ecs's Filter functions are immutable and can be
@@ -109,17 +109,18 @@ do
             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)
+                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(
+        local source = ('%s\nreturn function(system, e) return %s(%s) end')
+            :format(
                 table.concat(build, '\n'),
                 prefix,
-            table.concat(accum, seperator)
+                table.concat(accum, seperator))
-        )
         local loader, err = loadstring(source)
         if err then error(err) end
         return loader(...)
@@ -137,12 +138,14 @@ do
             subParts[#subParts + 1] = buildPart(p:sub(2, -2))
             return ('\255%d'):format(#subParts)
         end)
-        for invert, part, sep in str:gmatch('(%!?)([^%|%&%!]+)([%|%&%!]?)') do
+        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])
+                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 '==')
+                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 ')
@@ -152,7 +155,8 @@ do
     end
 
     function filterBuildString(str)
-        local source = ("return function(_, e) return %s end"):format(buildPart(str))
+        local source = ("return function(_, e) return %s end")
+            :format(buildPart(str))
         local loader, err = loadstring(source)
         if err then
             error(err)
@@ -190,11 +194,11 @@ end
 --
 --   * 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'.
+--   * Tokens can be prefixed with !, and are then inverted.
 --
 -- 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' OR 'b' OR 'c'.
---    'a&!b&c' - Matches entities with an 'a' component AND NOT a 'b' component AND a 'c' component.
+--    'a&!b&c' - Matches entities with an 'a' AND NOT 'b' AND 'c'.
 --    'a|(b&c&d)|e - Matches 'a' OR ('b' AND 'c' AND 'd') OR 'e'
 -- @param pattern
 function tiny.filter(pattern)
@@ -224,6 +228,19 @@ end
 -- 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.
+--   * `function system:preWrap(dt)` - Called on each system before update is
+-- called on any system.
+--   * `function system:postWrap(dt)` - Called on each system in reverse order
+-- after update is called on each system. The idea behind `preWrap` and
+-- `postWrap` is to allow for systems that modify the behavior of other systems.
+-- Say there is a DrawingSystem, which draws sprites to the screen, and a
+-- PostProcessingSystem, that adds some blur and bloom effects. In the preWrap
+-- method of the PostProcessingSystem, the System could set the drawing target
+-- for the DrawingSystem to a special buffer instead the screen. In the postWrap
+-- method, the PostProcessingSystem could then modify the buffer and render it
+-- to the screen. In this setup, the PostProcessingSystem would be added to the
+-- World after the drawingSystem (A similar but less flexible behavior could
+-- be accomplished with a single custom update function in the DrawingSystem).
 --
 -- 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
@@ -259,6 +276,16 @@ end
 -- in the next update, if it has one. This is usually managed by tiny-ecs, so
 -- users should mostly ignore this, too.
 --
+-- There is another option to (hopefully) increase performance in systems that
+-- have items added to or removed from them often, and have lots of entities in
+-- them.  Setting the `nocache` field of the system might improve performance.
+-- It is still experimental. There are some restriction to systems without
+-- caching, however.
+--
+--   * There is no `entities` table.
+--   * Callbacks such onAdd, onRemove, and onModify will never be called
+--   * Noncached systems cannot be sorted (There is no entities list to sort).
+--
 -- @section System
 
 -- Use an empty table as a key for identifying Systems. Any table that contains
@@ -281,21 +308,32 @@ local function processingSystemUpdate(system, dt)
     end
 
     if process then
-        local entities = system.entities
+        if system.nocache then
-        local len = #entities
+            local entities = system.world.entities
-        for i = 1, len do
+            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 function sortedSystemOnModify(system)
     local entities = system.entities
     local indices = system.indices
     local sortDelegate = system.sortDelegate
@@ -308,8 +346,7 @@ local function sortedSystemOnModify(system, dt)
     end
     tsort(entities, sortDelegate)
     for i = 1, #entities do
-        local entity = entities[i]
+        indices[entities[i]] = i
-        indices[entity] = i
     end
 end
 
@@ -386,9 +423,6 @@ local worldMetaTable
 function tiny.world(...)
     local ret = setmetatable({
 
-        -- List of Entities to add
-        entitiesToAdd = {},
-
         -- List of Entities to remove
         entitiesToRemove = {},
 
@@ -404,11 +438,9 @@ function tiny.world(...)
         -- Set of Entities
         entities = {},
 
-        -- Number of Entities in World
-        entityCount = 0,
-
         -- List of Systems
         systems = {}
+
     }, worldMetaTable)
 
     tiny_add(ret, ...)
@@ -422,13 +454,8 @@ end
 -- 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
-    end
     return entity
 end
 tiny_addEntity = tiny.addEntity
@@ -460,7 +487,7 @@ function tiny.add(world, ...)
 end
 tiny_add = tiny.add
 
---- Removes an Entity to the World. Returns the Entity.
+--- Removes an Entity from the World. Returns the Entity.
 function tiny.removeEntity(world, entity)
     local e2r = world.entitiesToRemove
     e2r[#e2r + 1] = entity
@@ -492,7 +519,6 @@ function tiny.remove(world, ...)
     end
     return ...
 end
-tiny_remove = tiny.remove
 
 -- Adds and removes Systems that have been marked from the World.
 function tiny_manageSystems(world)
@@ -506,7 +532,7 @@ function tiny_manageSystems(world)
     world.systemsToAdd = {}
     world.systemsToRemove = {}
 
-    local entities = world.entities
+    local worldEntityList = world.entities
     local systems = world.systems
 
     -- Remove Systems
@@ -514,7 +540,7 @@ function tiny_manageSystems(world)
         local system = s2r[i]
         local index = system.index
         local onRemove = system.onRemove
-        if onRemove then
+        if onRemove and not system.nocache then
             local entityList = system.entities
             for j = 1, #entityList do
                 onRemove(system, entityList[j])
@@ -540,11 +566,11 @@ function tiny_manageSystems(world)
     -- Add Systems
     for i = 1, #s2a do
         local system = s2a[i]
-        if systems[system.index] ~= system then
+        if systems[system.index or 0] ~= system then
-            local entityList = {}
+            if not system.nocache then
-            local entityIndices = {}
+                system.entities = {}
-            system.entities = entityList
+                system.indices = {}
-            system.indices = entityIndices
+            end
             if system.active == nil then
                 system.active = true
             end
@@ -559,10 +585,14 @@ function tiny_manageSystems(world)
             end
 
             -- Try to add Entities
+            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
                             local entityIndex = #entityList + 1
                             entityList[entityIndex] = entity
@@ -574,6 +604,7 @@ function tiny_manageSystems(world)
                     end
                 end
             end
+        end
         s2a[i] = nil
     end
 end
@@ -581,29 +612,32 @@ end
 -- Adds, removes, and changes Entities that have been marked.
 function tiny_manageEntities(world)
 
-    local e2a = world.entitiesToAdd
     local e2r = world.entitiesToRemove
     local e2c = world.entitiesToChange
 
     -- Early exit
-    if #e2a == 0 and #e2r == 0 and #e2c == 0 then
+    if #e2r == 0 and #e2c == 0 then
         return
     end
 
     world.entitiesToChange = {}
-    world.entitiesToAdd = {}
     world.entitiesToRemove = {}
 
     local entities = world.entities
     local systems = world.systems
-    local entityCount = world.entityCount
 
     -- Change Entities
     for i = 1, #e2c do
         local entity = e2c[i]
-        if entities[entity] then
+        -- Add if needed
+        if not entities[entity] then
+            local index = #entities + 1
+            entities[entity] = index
+            entities[index] = entity
+        end
         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]
@@ -639,11 +673,19 @@ function tiny_manageEntities(world)
     -- Remove Entities
     for i = 1, #e2r do
         local entity = e2r[i]
-        if entities[entity] then
+        e2r[i] = nil
+        local listIndex = entities[entity]
+        if listIndex then
+            -- Remove Entity from world state
+            local lastEntity = entities[#entities]
+            entities[lastEntity] = listIndex
             entities[entity] = nil
-            entityCount = entityCount - 1
+            entities[listIndex] = lastEntity
+            entities[#entities] = nil
+            -- 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]
@@ -661,38 +703,9 @@ function tiny_manageEntities(world)
                     end
                 end
             end
-        e2r[i] = nil
-    end
-
-    -- Add Entities
-    for i = 1, #e2a do
-        local entity = e2a[i]
-        if not entities[entity] then
-            entities[entity] = true
-            entityCount = entityCount + 1
-            for j = 1, #systems do
-                local system = systems[j]
-                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
-        e2a[i] = nil
-    end
-
-    -- Update Entity count
-    world.entityCount = entityCount
-end
 
 --- Manages Entities and Systems marked for deletion or addition. Call this
 -- before modifying Systems and Entities outside of a call to `tiny.update`.
@@ -700,6 +713,17 @@ end
 function tiny.refresh(world)
     tiny_manageSystems(world)
     tiny_manageEntities(world)
+    local systems = world.systems
+    for i = #systems, 1, -1 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`,
@@ -713,16 +737,27 @@ function tiny.update(world, dt, filter)
 
     local systems = world.systems
 
-    --  Iterate through Systems IN ORDER
+    -- Iterate through Systems IN REVERSE ORDER
-    for i = 1, #systems do
+    for i = #systems, 1, -1 do
         local system = systems[i]
-        if system.active and ((not filter) or filter(world, system)) then
+        if system.active then
-
             -- Call the modify callback on Systems that have been modified.
             local onModify = system.onModify
             if onModify and system.modified then
                 onModify(system, dt)
             end
+            local preWrap = system.preWrap
+            if preWrap and
+                ((not filter) or filter(world, system)) then
+                preWrap(system, dt)
+            end
+        end
+    end
+
+    --  Iterate through Systems IN ORDER
+    for i = 1, #systems do
+        local system = systems[i]
+        if system.active and ((not filter) or filter(world, system)) then
 
             -- Update Systems that have an update method (most Systems)
             local update = system.update
@@ -732,10 +767,8 @@ function tiny.update(world, dt, filter)
                     local bufferedTime = (system.bufferedTime or 0) + dt
                     while bufferedTime >= interval do
                         bufferedTime = bufferedTime - interval
-                        if update then
                         update(system, interval)
                     end
-                    end
                     system.bufferedTime = bufferedTime
                 else
                     update(system, dt)
@@ -745,12 +778,24 @@ function tiny.update(world, dt, filter)
             system.modified = false
         end
     end
+
+    -- Iterate through Systems IN ORDER AGAIN
+    for i = 1, #systems do
+        local system = systems[i]
+        local postWrap = system.postWrap
+        if postWrap and system.active and
+            ((not filter) or filter(world, system)) then
+            postWrap(system, dt)
+        end
+    end
+
 end
 
 --- Removes all Entities from the World.
 function tiny.clearEntities(world)
-    for e in pairs(world.entities) do
+    local el = world.entities
-        tiny_removeEntity(world, e)
+    for i = 1, #el do
+        tiny_removeEntity(world, el[i])
     end
 end
 
@@ -764,24 +809,19 @@ end
 
 --- Gets number of Entities in the World.
 function tiny.getEntityCount(world)
-    return world.entityCount
+    return #world.entities
 end
 
 --- Gets number of Systems in World.
 function tiny.getSystemCount(world)
-    return #(world.systems)
+    return #world.systems
-end
-
---- Gets the index of the System in the World.
--- A simpler alternative is `system.index`.
-function tiny.getSystemIndex(world, system)
-    return system.index
 end
 
 --- Sets the index of a System in the World, and returns the old index. Changes
 -- the order in which they Systems processed, because lower indexed Systems are
 -- processed first. Returns the old system.index.
 function tiny.setSystemIndex(world, system, index)
+    tiny_manageSystems(world)
     local oldIndex = system.index
     local systems = world.systems
 
@@ -814,10 +854,9 @@ worldMetaTable = {
         clearSystems = tiny.clearSystems,
         getEntityCount = tiny.getEntityCount,
         getSystemCount = tiny.getSystemCount,
-        getSystemIndex = tiny.getSystemIndex,
         setSystemIndex = tiny.setSystemIndex
     },
-    __tostring = function(self)
+    __tostring = function()
         return "<tiny-ecs_World>"
     end
 }