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|
--- Provides a reuseable and convenient framework for creating classes in Lua.
-- Two possible notations:
--
-- B = class(A)
-- class.B(A)
--
-- The latter form creates a named class.
--
-- See the Guide for further @{01-introduction.md.Simplifying_Object_Oriented_Programming_in_Lua|discussion}
-- @module pl.class
local error, getmetatable, io, pairs, rawget, rawset, setmetatable, tostring, type =
_G.error, _G.getmetatable, _G.io, _G.pairs, _G.rawget, _G.rawset, _G.setmetatable, _G.tostring, _G.type
-- this trickery is necessary to prevent the inheritance of 'super' and
-- the resulting recursive call problems.
local function call_ctor (c,obj,...)
-- nice alias for the base class ctor
local base = rawget(c,'_base')
if base then
local parent_ctor = rawget(base,'_init')
if parent_ctor then
obj.super = function(obj,...)
call_ctor(base,obj,...)
end
end
end
local res = c._init(obj,...)
obj.super = nil
return res
end
local function is_a(self,klass)
local m = getmetatable(self)
if not m then return false end --*can't be an object!
while m do
if m == klass then return true end
m = rawget(m,'_base')
end
return false
end
local function class_of(klass,obj)
if type(klass) ~= 'table' or not rawget(klass,'is_a') then return false end
return klass.is_a(obj,klass)
end
local function _class_tostring (obj)
local mt = obj._class
local name = rawget(mt,'_name')
setmetatable(obj,nil)
local str = tostring(obj)
setmetatable(obj,mt)
if name then str = name ..str:gsub('table','') end
return str
end
local function tupdate(td,ts)
for k,v in pairs(ts) do
td[k] = v
end
end
local function _class(base,c_arg,c)
c = c or {} -- a new class instance, which is the metatable for all objects of this type
-- the class will be the metatable for all its objects,
-- and they will look up their methods in it.
local mt = {} -- a metatable for the class instance
if type(base) == 'table' then
-- our new class is a shallow copy of the base class!
tupdate(c,base)
c._base = base
-- inherit the 'not found' handler, if present
if rawget(c,'_handler') then mt.__index = c._handler end
elseif base ~= nil then
error("must derive from a table type",3)
end
c.__index = c
setmetatable(c,mt)
c._init = nil
if base and rawget(base,'_class_init') then
base._class_init(c,c_arg)
end
-- expose a ctor which can be called by <classname>(<args>)
mt.__call = function(class_tbl,...)
local obj = {}
setmetatable(obj,c)
if rawget(c,'_init') then -- explicit constructor
local res = call_ctor(c,obj,...)
if res then -- _if_ a ctor returns a value, it becomes the object...
obj = res
setmetatable(obj,c)
end
elseif base and rawget(base,'_init') then -- default constructor
-- make sure that any stuff from the base class is initialized!
call_ctor(base,obj,...)
end
if base and rawget(base,'_post_init') then
base._post_init(obj)
end
if not rawget(c,'__tostring') then
c.__tostring = _class_tostring
end
return obj
end
-- Call Class.catch to set a handler for methods/properties not found in the class!
c.catch = function(handler)
c._handler = handler
mt.__index = handler
end
c.is_a = is_a
c.class_of = class_of
c._class = c
return c
end
--- create a new class, derived from a given base class.
-- Supporting two class creation syntaxes:
-- either `Name = class(base)` or `class.Name(base)`
-- @function class
-- @param base optional base class
-- @param c_arg optional parameter to class ctor
-- @param c optional table to be used as class
local class
class = setmetatable({},{
__call = function(fun,...)
return _class(...)
end,
__index = function(tbl,key)
if key == 'class' then
io.stderr:write('require("pl.class").class is deprecated. Use require("pl.class")\n')
return class
end
local env = _G
return function(...)
local c = _class(...)
c._name = key
rawset(env,key,c)
return c
end
end
})
class.properties = class()
function class.properties._class_init(klass)
klass.__index = function(t,key)
-- normal class lookup!
local v = klass[key]
if v then return v end
-- is it a getter?
v = rawget(klass,'get_'..key)
if v then
return v(t)
end
-- is it a field?
return rawget(t,'_'..key)
end
klass.__newindex = function (t,key,value)
-- if there's a setter, use that, otherwise directly set table
local p = 'set_'..key
local setter = klass[p]
if setter then
setter(t,value)
else
rawset(t,key,value)
end
end
end
return class
|
