Re: multi-level inheritance and __index
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- Subject: Re: multi-level inheritance and __index
- From: Steven Degutis <sbdegutis@...>
- Date: 2015年1月14日 17:20:40 -0600
> I want to synthesize properties on the base class using __index and __newindex so that they're available to all instances.
To add methods to "all instances" of a class, you just add methods to
the table that's the __index field on every instance's metatable, like
so:
Sprite = {}
sprite1 = setmetatable({x=1}, {__index = Sprite})
sprite2 = setmetatable({x=2}, {__index = Sprite})
Sprite.foobar = function(self) return self.x * 10 end
-- alternatively but functionally equivalent:
function Sprite:foobar() return self.x * 10 end
sprite1:foobar() -- returns 10
sprite2:foobar() -- returns 20
To turn this into multi-level inheritance, you can just do this:
SpriteBase = {}
Sprite = setmetatable(Sprite, {__index = SpriteBase})
Now, just add methods to SpriteBase, and both sprite1 and sprite2 have them.