Usage lua5.4 beta in the to-be-closed variable

Corresponding to the latest lua5.4 beta version: 2019-10-09 Published

This function is modified twice before grammar, syntax currently no accident will be the final decision, there is no information on the latest Chinese, so I came here to send it.

First introduced to this function:

Are labeled to-be-closed local variables, it will be beyond the scope, call its __closed element method, which provides a C ++ destructor similar role for us.

It is marked as a to-be-closed variable should meet two prerequisites:

1, which is a table

2, has been designated __close element method for it

The current version Syntax: add <close> after the variable name, the variable is marked as to-be-closed variable

local t<close> = ...

Example:

test2 function () 
    local T = {X = . 1 }; 
    setmetatable (T, {__close = function (...) Print ( ' Close ' )} End); 
    local TC <Close> = T;
     - the function returns, automatically performing the method of tc __close element. 
End 
test2 ();

 - a file operation as an example:
 - in the absence of to-be- case closed variables: 
function foo ()
     - Open a file 
    local FD = io.open ( ' C: \\. 1. TXT ' , ' R & lt ' );

     - to read the file 
    local X = FD: read ( ' * A ');

     - Next, the file content is determined
     - if we need a variety of content on the logical
     IF X == ' . 1 ' the then 
        FD: Close (); 
        return ;
     the else  IF X == ' 2 ' the then 
        Print ( ' file contents: 2 ' ); 
        FD: Close (); 
        return ; 
    End 

    Print ( ' wrong file content: ' .. X-); 
    FD: Close (); 
End

 - to-BE- case of closed: 
foo2 function ()

     - Add <close> after the variable name 
    local fd<Close> = io.open ( ' C: \\ 1.txt ' , ' R & lt ' );
     - Then you have to write a return position and various super annoying fd: close () goodbye

     - Read take file 
    local X = FD: Read ( ' * A ' );
     IF X == ' . 1 ' the then
         return ;
     the else  IF X == ' 2 ' the then 
        Print ( ' file content: 2 ' );
         return ; 
    End 

    Print ( ' wrong file content: '.. X-); 

End

 - c ++ to achieve the std :: lock_guard for example:
 - xshare. Lock xshare.unlock from my other article: HTTPS: // www.cnblogs.com/babypapa/p/ 11711389.html 
function lock_guard (XT) 
    local T = {xstab = XT}; 
    setmetatable (T, {__close = function (Tab) xshare.unlock (tab.xstab)} End) 
    xshare. Lock (XT);
     return T; 
End 

foo3 function (XT) 
    local LG <Close> = lock_guard (XT); 
    ... 
End