[Lua]索引极致，form.lua

local form = {_tag = 'form'}
function form.build(tag, super)
    local target = {
        _tag = tag,
        _super = super
    }
    form.spec(target)
    setmetatable(target, form._meta())
    return target
end

function form.on(target, spec)
    local tar = {}
    for k,v in pairs(spec) do
        if type(v) == 'function' then
            local method = target[k] or spec[k]
            tar[k] = function ( ... )
                method(target, ...)
            end
        else
            tar[k] = v
        end
    end
    return tar
end

function form.spec(target)
    target.tag = target.tag or form.tag
    function target:on(target)
        local tar = {}
        local spec = self
        for k,v in pairs(spec) do
            if type(v) == 'function' then
                tar[k] = function ( ... )
                    spec[k](target, ...)
                end
            else
                tar[k] = v
            end
        end
        print(target:tag()..'['..spec._tag..'] target binding form produced')
        -- no such key binding to the target
        tar.on = nil
        tar.spec = nil
        return tar
    end
    function target:spec(prop, target)
        if  self._interface == nil then
            self._interface = {}
        end
        local handler = {}
        function handler.string(self, prop, target)
            if target ~= nil then
                print(self:tag()..'['..prop..'] setter/getter produced')
                local property = '_'..prop
                local function prop_(self, target)
                    if target ~= nil then
                        self[property] = target
                        return self
                    end
                    return self[property]
                end
                prop_(self, target)[prop] = prop_
            end
            local spec = self[prop](self)
            return spec and spec:on(self)
        end
        function handler.table(self, prop)
            local target = prop
            table.insert(self._interface, target)
            if type(target._tag)=='string' then
                print(self:tag()..' interface['..target._tag..'] specified')
            end
            return self
        end
        local handler_prop = handler[type(prop)]
        return handler_prop and handler_prop(self, prop, target)
    end
    return target
end

function form:tag()
    local tag = self._tag
    if type(tag)=='string'
    then
        return '*'..tag..'*'
    end
    return 'none.TAG'
end

function form._meta()
    local meta = {}
    function meta.__index(target, key)
        -- avoid target._interface rise to C stack overflow, .etc
        -- following anonymous table specify the key filters
        if ({_interface = true, _super = true})[key] then return nil end

        local super = target._super
        local interface = target._interface
        local v = super and super[key]
        if v == nil and type(interface)=='table'
        then
            for i=1, #interface do
                v = interface[i][key]
                if v ~= nil then return v end
            end
        end
        return v
    end
    return meta
end

return form