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classlib.lua
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executable file
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-- classlib.lua 2.03
-- PRIVATE
--[[
Define unique value for identifying ambiguous base objects and inherited
attributes. Ambiguous values are normally removed from classes and objects,
but if keep_ambiguous == true they are left there and the ambiguous value
is made to behave in a way useful for debugging.
]]
local ambiguous = { __type = 'ambiguous' }
local remove_ambiguous
if keep_ambiguous then
-- Make ambiguous complain about everything except tostring()
local function invalid(operation)
return function()
error('Invalid ' .. operation .. ' on ambiguous')
end
end
local ambiguous_mt =
{
__add = invalid('addition'),
__sub = invalid('substraction'),
__mul = invalid('multiplication'),
__div = invalid('division'),
__mod = invalid('modulus operation'),
__pow = invalid('exponentiation'),
__unm = invalid('unary minus'),
__concat = invalid('concatenation'),
__len = invalid('length operation'),
__eq = invalid('equality comparison'),
__lt = invalid('less than'),
__le = invalid('less or equal'),
__index = invalid('indexing'),
__newindex = invalid('new indexing'),
__call = invalid('call'),
__tostring = function() return 'ambiguous' end,
__tonumber = invalid('conversion to number')
}
setmetatable(ambiguous, ambiguous_mt)
-- Don't remove ambiguous values from classes and objects
remove_ambiguous = function() end
else
-- Remove ambiguous values from classes and objects
remove_ambiguous = function(t)
for k, v in pairs(t) do
if v == ambiguous then t[k] = nil end
end
end
end
--[[
Reserved attribute names.
]]
local reserved =
{
__index = true,
__newindex = true,
__type = true,
__class = true,
__bases = true,
__inherited = true,
__from = true,
__shared = true,
__user_init = true,
__name = true,
__initialized = true
}
--[[
Some special user-set attributes are renamed.
]]
local rename =
{
__init = '__user_init',
__set = '__user_set',
__get = '__user_get'
}
--[[
The metatable of all classes, containing:
To be used by the classes:
__call() for creating instances
__init() default constructor
is_a() for checking object and class types
implements() for checking interface support
For internal use:
__newindex() for controlling class population
]]
local class_mt = {}
class_mt.__index = class_mt
--[[
This controls class population.
Here 'self' is a class being populated by inheritance or by the user.
]]
function class_mt:__newindex(name, value)
-- Rename special user-set attributes
if rename[name] then name = rename[name] end
-- __user_get() needs an __index() handler
if name == '__user_get' then
self.__index = value and function(obj, k)
local v = self[k]
if v == nil and not reserved[k] then v = value(obj, k) end
return v
end or self
-- __user_set() needs a __newindex() handler
elseif name == '__user_set' then
self.__newindex = value and function(obj, k, v)
if reserved[k] or not value(obj, k, v) then rawset(obj, k, v) end
end or nil
end
-- Assign the attribute
rawset(self, name, value)
end
--[[
This function creates an object of a certain class and calls itself
recursively to create one child object for each base class. Base objects
of unnamed base classes are accessed by using the base class as an index
into the object, base objects of named base classes are accessed as fields
of the object with the names of their respective base classes.
Classes derived in shared mode will create only a single base object.
Unambiguous grandchildren are inherited by the parent if they do not
collide with direct children.
]]
local function build(class, shared_objs, shared)
-- Repository for storing shared objects
shared_objs = shared_objs or {}
-- Shared inheritance creates a single shared child per base class
if shared and shared_objs[class] then return shared_objs[class] end
-- New object
local obj = { __type = 'object' }
-- Repository for storing inherited base objects
local inherited = {}
-- Build child objects for each base class
for i, base in ipairs(class.__bases) do
local child = build(base, shared_objs, class.__shared[base])
obj[base.__name] = child
-- Get inherited grandchildren from this child
for c, grandchild in pairs(child) do
-- We can only accept one inherited grandchild of each class,
-- otherwise this is an ambiguous reference
if not inherited[c] then inherited[c] = grandchild
elseif inherited[c] ~= grandchild then inherited[c] = ambiguous
end
end
end
-- Accept inherited grandchildren if they don't collide with
-- direct children
for k, v in pairs(inherited) do
if not obj[k] then obj[k] = v end
end
-- Remove ambiguous inherited grandchildren
remove_ambiguous(obj)
-- Object is ready
setmetatable(obj, class)
-- If shared, add it to the repository of shared objects
if shared then shared_objs[class] = obj end
return obj
end
--[[
The __call() operator creates an instance of the class and initializes it.
]]
function class_mt:__call(...)
local obj = build(self)
obj:__init(...)
return obj
end
--[[
The implements() method checks that an object or class supports the
interface of a target class. This means it can be passed as an argument to
any function that expects the target class. We consider only functions
and callable objects to be part of the interface of a class.
]]
function class_mt:implements(class)
-- Auxiliary function to determine if something is callable
local function is_callable(v)
if v == ambiguous then return false end
if type(v) == 'function' then return true end
local mt = getmetatable(v)
return mt and type(mt.__call) == 'function'
end
-- Check we have all the target's callables (except reserved names)
for k, v in pairs(class) do
if not reserved[k] and is_callable(v) and not is_callable(self[k]) then
return false
end
end
return true
end
--[[
The is_a() method checks the type of an object or class starting from
its class and following the derivation chain upwards looking for
the target class. If the target class is found, it checks that its
interface is supported (this may fail in multiple inheritance because
of ambiguities).
]]
function class_mt:is_a(class)
-- If our class is the target class this is trivially true
if self.__class == class then return true end
-- Auxiliary function to determine if a target class is one of a list of
-- classes or one of their bases
local function find(target, classlist)
for i, class in ipairs(classlist) do
if class == target or find(target, class.__bases) then
return true
end
end
return false
end
-- Check that we derive from the target
if not find(class, self.__bases) then return false end
-- Check that we implement the target's interface.
return self:implements(class)
end
--[[
Factory-supplied constructor, calls the user-supplied constructor if any,
then calls the constructors of the bases to initialize those that were
not initialized before. Objects are initialized exactly once.
]]
function class_mt:__init(...)
if self.__initialized then return end
if self.__user_init then self:__user_init(...) end
for i, base in ipairs(self.__bases) do
self[base.__name]:__init(...)
end
self.__initialized = true
end
-- PUBLIC
--[[
Utility type and interface checking functions
]]
function typeof(value)
local t = type(value)
return t =='table' and value.__type or t
end
function classof(value)
local t = type(value)
return t == 'table' and value.__class or nil
end
function classname(value)
if not classof(value) then return nil end
local name = value.__name
return type(name) == 'string' and name or nil
end
function implements(value, class)
return classof(value) and value:implements(class) or false
end
function is_a(value, class)
return classof(value) and value:is_a(class) or false
end
--[[
Use a table to control class creation and naming.
]]
class = {}
local mt = {}
setmetatable(class, mt)
--[[
Create a named or unnamed class by calling class([name, ] ...).
Arguments are an optional string to set the class name and the classes or
shared classes to be derived from.
]]
function mt:__call(...)
local arg = {...}
-- Create a new class
local c =
{
__type = 'class',
__bases = {},
__shared = {}
}
c.__class = c
c.__index = c
-- A first string argument sets the name of the class.
if type(arg[1]) == 'string' then
c.__name = arg[1]
table.remove(arg, 1)
else
c.__name = c
end
-- Repository of inherited attributes
local inherited = {}
local from = {}
-- Inherit from the base classes
for i, base in ipairs(arg) do
-- Get the base and whether it is inherited in shared mode
local basetype = typeof(base)
local shared = basetype == 'share'
assert(basetype == 'class' or shared,
'Base ' .. i .. ' is not a class or shared class')
if shared then base = base.__class end
-- Just in case, check this base is not repeated
assert(c.__shared[base] == nil, 'Base ' .. i .. ' is duplicated')
-- Accept it
c.__bases[i] = base
c.__shared[base] = shared
-- Get attributes that could be inherited from this base
for k, v in pairs(base) do
-- Skip reserved and ambiguous attributes
if not reserved[k] and v ~= ambiguous and
inherited[k] ~= ambiguous then
-- Where does this attribute come from?
local new_from
-- Check if the attribute was inherited by the base
local base_inherited = base.__inherited[k]
if base_inherited then
-- If it has been redefined, cancel this inheritance
if base_inherited ~= v then -- (1)
base.__inherited[k] = nil
base.__from[k] = nil
-- It is still inherited, get it from the original
else
new_from = base.__from[k]
end
end
-- If it is not inherited by the base, it originates there
new_from = new_from or { class = base, shared = shared }
-- Accept a first-time inheritance
local current_from = from[k]
if not current_from then
from[k] = new_from
-- Wrap methods so that they are called with the correct
-- base object self. For functions that are not methods
-- this creates some useless code.
if type(v) == 'function' then
local origin = new_from.class
inherited[k] = function(self, ...)
return origin[k](self[origin.__name], ...)
end
-- Properties are copied
else
inherited[k] = v
end
-- Attributes inherited more than once are ambiguous unless
-- they originate in the same shared class.
elseif current_from.class ~= new_from.class or
not current_from.shared or not new_from.shared then
inherited[k] = ambiguous
from[k] = nil
end
end
end
end
-- Remove ambiguous inherited attributes
remove_ambiguous(inherited)
-- Set the metatable now, it monitors attribute setting and does some
-- special processing for some of them.
setmetatable(c, class_mt)
-- Set inherited attributes in the class, they may be redefined afterwards
for k, v in pairs(inherited) do c[k] = v end -- checked at (1)
c.__inherited = inherited
c.__from = from
return c
end
--[[
Create a named class and assign it to a global variable of the same name.
Example: class.A(...) is equivalent to (global) A = class('A', ...).
]]
function mt:__index(name)
return function(...)
local c = class(name, ...)
getfenv()[name] = c
return c
end
end
--[[
Wrap a class for shared derivation.
]]
function shared(class)
assert(typeof(class) == 'class', 'Argument is not a class')
return { __type = 'share', __class = class }
end