list - Lua DSL 还是聪明的闭包？

Question

我正在尝试使用 Lua 并尝试实现一些列表处理逻辑。我不确定我是否真正掌握了协程和匿名函数的力量，但我正在尝试。我知道这些东西在 Ruby/Groovy/Javascript 等其他脚本语言中是如何工作的，我想在 Lua 中做一些同样聪明的事情。这是我提出的一个例子:

model = { { player = "Cliff", age = 35, gender = "male" }, { player = "Ally", age = 36, gender = "female" }, { player = "Jasmine", age = 13, gender = "female" }, { player = "Lauren", age = 6.5, gender = "female" } }

function allplayers()
    return coroutine.create(function()
        for idx, each in ipairs(model) do
            coroutine.yield(idx, each)
        end
    end)
end

function handlePlayers(source)
    local status, idx, each = coroutine.resume(source)
    while each do
        print(idx, each.player)
        status, idx, each = coroutine.resume(source)
    end
end

function having(source, predicate)
    return coroutine.create(function()
        local status, idx, each = coroutine.resume(source)
        while each do
            if predicate(each)  then
                coroutine.yield(idx, each)
            end
            status, idx, each = coroutine.resume(source)
        end
    end)
end

handlePlayers(having(allplayers(), function(each) return each.age < 30 end))

理想情况下，我希望能够编写如下代码:

allplayers(having(function(each) return each.age < 30 end))

甚至更好:

allplayers(having({each.age < 30 }))

产生相同的输出，但我无法完全理解如何或什至可以做到这一点。我上面的所有迭代和循环以及所有内容似乎都过于多余。有没有更好的方法来做到这一点？ (男孩，我想念在 Groovy 中编码，因为总有一种更时髦的方式来做某事......)

Answer 1

如果您不需要重用过滤后的结果，请考虑使用迭代器:

model = {
  { player = "Cliff", age = 35, gender = "male" },
  { player = "Ally", age = 36, gender = "female" },
  { player = "Jasmine", age = 13, gender = "female" },
  { player = "Lauren", age = 6.5, gender = "female" }
}

function model:having(predicate)
    local index = 0 
    return function()
        while true do
            index = index + 1
            if index > #self then break end
            if predicate(self[index]) then return self[index] end
        end
    end
end

for item in model:having(function(m) return m.age < 30 end) do
    print(item.player)
end