設計連結串列，並設計其迭代函式

生成連結串列、列印連結串列

arr = {10, 20, 30, 100, 101, 88, 50};
head = nil;
local i = 1
while true do 
    if arr[i] then
        head = {value = arr[i], next = head};   ---從右往左執行的
        --[[
            head表實際儲存的資料是這樣的
            {value = 50, next = {value = 88 ,next = { value = 101 , next = {value = 100 ,next = nil}}}}
        ]]
        i = i + 1;
    else
        break;
    end
end


while head do
    print(head.value);
    head = head.next;
end

----------------------------------------
output:
50
88
101
100
30
20
10
 

用無狀態迭代器來實現

function iterator(head,next)
    if next == nil then 
        return head;
    else
        return next.next;
    end
end



function traverse(head)
    return  iterator,head,nil;   --實際是給_f(_s,_v)呼叫的
end


for v in traverse(head) do 
    print(v.value);
end
---------------------------------------
output:
50
88
101
100
30
20
10
 

用有狀態迭代器來實現

function iterator(head) 
    local next = nil;
    return function ()
        if next == nil then 
            next = head;
            return next;
        else
            next = next.next;
            return next;
        end
    end
end



for k,v in iterator(head) do
    print(k.value);
end
----------------------------------------
output：
50
88
101
100
30
20
10
 

for原型分析

arr = {10, 20, 30, 100, 101, 88, 50};
head = nil;
local i = 1
while true do 
    if arr[i] then
        head = {value = arr[i], next = head};   ---從右往左執行的
        --[[
            head表實際儲存的資料是這樣的
            {value = 50, next = {value = 88 ,next = { value = 101 , next = {value = 100 ,next = nil}}}}
        ]]
        i = i + 1;
    else
        break;
    end
end


function iterator(head) 
    local next = nil;
    return function ()
        if next == nil then 
            next = head;
            return next;
        else
            next = next.next;
            return next;
        end
    end
end


do
    local _f, _s, _v = iterator(head);  
    --[[
         local _f, _s, _v = iterator(head); 
        引用iterator(head)函式，第一次返回_f, _s和_v都是nil,_f實際就是iterator裡面返回的函式，
        next初始化等於nil，nil相當於一個static變數，會一直在這個迴圈結束前儲存變化next的變數，
    ]]
    while true do
        local k,v = _f(_s,_v);            ----iterator(head,nil)   2: iterator(nil, head)
        --[[
            local k,v = _f(_s,_v);
            _f呼叫的時候傳遞的兩個引數是nil,nil，第一次執行next=nil，返回head，把next賦值head
            第二次執行的時候next=head,返回了next.next，等價於head.next，
        ]]
        _v = k;                           ----- _v = head; 
        --[[
            _v = k;
            把返回的值賦值給_v，再次帶入迴圈
        ]]
        if k == nil then break; end
        print(k.value);
    end
end
--------------------------------------------------------
output:
50
88
101
100
30
20
10