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

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

@@ -1,29 +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.
-Because of lua's tabular nature, Entity Component Systems are a natural choice
+[![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.
+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.
-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.
+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
+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
-should contain primarily data rather than code, as it is the Systems's job to
+Entities are simply Lua tables of data that gets processed by Systems. Entities
+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
-number in `tiny._VERSION`, while other commits will just have the string 'scm'.
+please use a tagged release or use LuaRocks.
 
 ## 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

@@ -0,0 +1,24 @@
+package = "tiny-ecs"
+version = "1.3-1"
+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-1.3-2.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

@@ -90,6 +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()
@@ -190,9 +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())
@@ -227,21 +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

@@ -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
@@ -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
-local tiny = { _VERSION = "1.2-1" }
+-- @copyright 2016
+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
@@ -85,88 +85,125 @@ 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 = ('%s\nreturn function(system, e) return %s(%s) 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
-    end
+    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 inverted.
+--
+-- Examples are best:
+--    'a|b|c' - Matches entities with an 'a' OR 'b' OR 'c'.
+--    '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)
+    local state, value = pcall(filterBuildString, pattern)
+    if state then return value else return nil, value end
 end
 
 --- System functions.
@@ -191,6 +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
@@ -226,6 +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
@@ -248,11 +308,22 @@ local function processingSystemUpdate(system, dt)
     end
 
     if process then
-        local entities = system.entities
-        local len = #entities
-        for i = 1, len do
-            local entity = entities[i]
-            process(system, entity, dt)
+        if system.nocache then
+            local entities = system.world.entities
+            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
 
@@ -261,8 +332,8 @@ local function processingSystemUpdate(system, dt)
     end
 end
 
--- Sorts Systems by a function system.sort(entity1, entity2) on modify.
-local function sortedSystemOnModify(system, dt)
+-- Sorts Systems by a function system.sortDelegate(entity1, entity2) on modify.
+local function sortedSystemOnModify(system)
     local entities = system.entities
     local indices = system.indices
     local sortDelegate = system.sortDelegate
@@ -275,8 +346,7 @@ 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
 
@@ -353,9 +423,6 @@ local worldMetaTable
 function tiny.world(...)
     local ret = setmetatable({
 
-        -- List of Entities to add
-        entitiesToAdd = {},
-
         -- List of Entities to remove
         entitiesToRemove = {},
 
@@ -371,11 +438,9 @@ function tiny.world(...)
         -- Set of Entities
         entities = {},
 
-        -- Number of Entities in World
-        entityCount = 0,
-
         -- List of Systems
         systems = {}
+
     }, worldMetaTable)
 
     tiny_add(ret, ...)
@@ -389,13 +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
+    local e2c = world.entitiesToChange
+    e2c[#e2c + 1] = entity
     return entity
 end
 tiny_addEntity = tiny.addEntity
@@ -427,7 +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
@@ -459,7 +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)
@@ -473,7 +532,7 @@ function tiny_manageSystems(world)
     world.systemsToAdd = {}
     world.systemsToRemove = {}
 
-    local entities = world.entities
+    local worldEntityList = world.entities
     local systems = world.systems
 
     -- Remove Systems
@@ -481,7 +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])
@@ -507,11 +566,11 @@ function tiny_manageSystems(world)
     -- Add Systems
     for i = 1, #s2a do
         local system = s2a[i]
-        if systems[system.index] ~= system then
-            local entityList = {}
-            local entityIndices = {}
-            system.entities = entityList
-            system.indices = entityIndices
+        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
@@ -526,16 +585,21 @@ function tiny_manageSystems(world)
             end
 
             -- Try to add Entities
-            local onAdd = system.onAdd
-            local filter = system.filter
-            if filter then
-                for entity in pairs(entities) do
-                    if filter(system, entity) then
-                        local entityIndex = #entityList + 1
-                        entityList[entityIndex] = entity
-                        entityIndices[entity] = entityIndex
-                        if onAdd then
-                            onAdd(system, entity)
+            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 j = 1, #worldEntityList do
+                        local entity = worldEntityList[j]
+                        if filter(system, entity) then
+                            local entityIndex = #entityList + 1
+                            entityList[entityIndex] = entity
+                            entityIndices[entity] = entityIndex
+                            if onAdd then
+                                onAdd(system, entity)
+                            end
                         end
                     end
                 end
@@ -548,29 +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
-            for j = 1, #systems do
-                local system = systems[j]
+        -- 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]
@@ -606,59 +673,38 @@ function tiny_manageEntities(world)
     -- Remove Entities
     for i = 1, #e2r do
         local entity = e2r[i]
-        if entities[entity] then
-            entities[entity] = nil
-            entityCount = entityCount - 1
-            for j = 1, #systems do
-                local system = systems[j]
-                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
         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
+        local listIndex = entities[entity]
+        if listIndex then
+            -- Remove Entity from world state
+            local lastEntity = entities[#entities]
+            entities[lastEntity] = listIndex
+            entities[entity] = nil
+            entities[listIndex] = lastEntity
+            entities[#entities] = nil
+            -- Remove from cached systems
             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)
+                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
-        e2a[i] = nil
     end
-
-    -- Update Entity count
-    world.entityCount = entityCount
 end
 
 --- Manages Entities and Systems marked for deletion or addition. Call this
@@ -667,6 +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`,
@@ -680,16 +737,27 @@ function tiny.update(world, dt, filter)
 
     local systems = world.systems
 
-    --  Iterate through Systems IN ORDER
-    for i = 1, #systems do
+    -- Iterate through Systems IN REVERSE ORDER
+    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
@@ -699,9 +767,7 @@ 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
+                        update(system, interval)
                     end
                     system.bufferedTime = bufferedTime
                 else
@@ -712,12 +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
-        tiny_removeEntity(world, e)
+    local el = world.entities
+    for i = 1, #el do
+        tiny_removeEntity(world, el[i])
     end
 end
 
@@ -731,24 +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)
-end
-
---- Gets the index of the System in the World.
--- A simpler alternative is `system.index`.
-function tiny.getSystemIndex(world, system)
-    return system.index
+    return #world.systems
 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
 
@@ -781,10 +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
 }