lua以xpcall實作try/catch功能

-- 列印錯誤資訊
local function __TRACKBACK__(errmsg)
    local track_text = debug.traceback(tostring(errmsg), 6);
    print("---------------------------------------- TRACKBACK ----------------------------------------");
    print(track_text, "LUA ERROR");
    print("---------------------------------------- TRACKBACK ----------------------------------------");
    local exception_text = "LUA EXCEPTION\n" .. track_text;
    return false;
end

--[[ 嘗試調一個function 這個function可以帶可變參數
如果被調用的函數有異常 傳回false，退出此方法繼續執行其他代碼并列印出異常資訊；]]
function trycall(func, ...)
    local args = { ... };
    return xpcall(function() func(unpack(args)) end, __TRACKBACK__);
end
--測試代碼：

trycall(function(param)
　　　　　　print("message "..param)
　　　　　　print("message "..nil)
        end, "test trycall")      

##輸出結果如下：

>lua -e "io.stdout:setvbuf 'no'" "itertor_test.lua"

message test trycall

---------------------------------------- TRACKBACK ----------------------------------------

itertor_test.lua:45: attempt to concatenate a nil value

stack traceback:

itertor_test.lua:43: in main chunk

[C]: ? LUA ERROR

>Exit code: 0

xpcall (f, err)

This function is similar to 

pcall

,except that you can set a new error handler.

xpcall

 calls function 

f

 in protected mode,using 

err

 as the error handler.Any error inside 

f

 is not propagated;instead, 

xpcall

 catches the error,calls the 

err

 function with the original error object,and returns a status code.Its first result is the status code (a boolean),which is true if the call succeeds without errors.In this case, 

xpcall

 also returns all results from the call,after this first result.In case of any error,

xpcall

 returns false plus the result from 

err

.