我创建了一个与此处所示类似的函数,但在__add元方法方面遇到了问题。我希望能够在一个类的两个实例上使用__add元方法,但唯一可行的方法似乎是将元方法添加到实例的元表中。有没有一种方法可以将其设置为工作,这样我的类或其元表就可以使用__add元方法,并在一起添加实例时工作?
function Class(superClass, constructor)
local class = {};
local metatable = {};
if superClass then
metatable.__index = superClass;
end
setmetatable(class, metatable);
function metatable:__call(...)
local instance = {};
setmetatable(instance, { __index = class });
if class.constructor then
class.constructor(instance, ...);
end
return instance;
end
class.constructor = constructor;
return class;
end
下面是我想做的一个例子:
A = Class(nil, function(self, num)
self.num = num;
end);
function A:__add(rhs)
return A(self.num + rhs.num);
end
a = A(1);
b = A(2);
c = a + b;
多亏了三十二上校和埃坦·雷斯纳的帮助,我想出了以下解决方案:
function metatable.__call(self, ...)
local instance = {};
setmetatable(instance, self);
if class.constructor then
class.constructor(instance, ...);
end
return instance;
end
我更改了函数,使其不再隐藏自变量,并将其用作实例的元表。添加现在可以按预期工作。然而,它在其他地方引发了问题。
我尝试了一些在其他地方找到的东西,并提出了这个可行的解决方案:
function Class(superClass, constructor)
local class = {};
if superClass then
for k,v in pairs(superClass)
do
class[k] = v;
end
class._superClass = superClass;
end
class.__index = class;
local metatable = {};
function metatable:__call(...)
local instance = {};
setmetatable(instance, class);
if class.constructor then
class.constructor(instance, ...);
end
return instance;
end
class.constructor = constructor;
setmetatable(class, metatable);
return class;
end
为了以防万一,我通常是这样创建类的(也很容易支持继承):
function Vector(x, y)
local self = {}
self.x = x
self.y = y
self.magnitude = math.sqrt(x*x + y*y)
function self.unit()
return Vector(x/self.magnitude, y/self.magnitude)
end
function self.printComponents()
print("[" .. self.x .. ", " .. self.y .. "]")
end
--if you want to implement metamethods...
setmetatable(self, {
__add = function(_, other)
return Vector(self.x + other.x, self.y + other.y)
end
})
return self
end
-- now, let's make a ComplexNumber class that inherits from Vector
function ComplexNumber(a, b)
-- define self as an instance of Vector
local self = Vector(a, b)
-- override Vector.printComponents()
function self.printComponents()
print(self.x .. " + " .. self.y .. "i")
end
return self
end
--examples
local v = Vector(10, 20)
v.printComponents() --> [10, 20]
local c = ComplexNumber(10, 5)
c.printComponents() --> 10 + 5i