回收或重用变量可以接受吗？ [英] is it acceptable to recycle or reuse variables?

问题描述

我看到无处不在，我似乎无法以某种方式找到答案。是否可以（好或坏的做法）重用或回收变量？它工作，我已经使用这种方法几次，但我不知道我应该做这个不是。我试图摆脱使用静态方法，并进入依赖注入。

在这个例子中，$ table_name设置在其他地方。

  class DbObject {
 private $ db = NULL; 
 protected $ table_name; 
 
 public function __construct（$ dbh，$ item）{
 $ this-> db = $ dbh; 
 $ this-> $ table_name = $ item; 
} 
 
 //计算数据库中的项目// 
 public function count_all（）{
 try {
 $ sql ='SELECT COUNT（*） FROM'。 $这 - >表名; 
 
 $ stmt = $ this-> db-> query（$ sql）; 
 $ stmt-> setFetchMode（pdo :: FETCH_COLUMN，0）; 
 $ result = $ stmt-> fetchColumn（）; 
 return $ result; 
} catch（PDOException $ e）{
 echo $ e-> getMessage（））; 
} 
} 
  

要使用这个，我会使用它： / p>

  $ total_count = new DbObject（new Database（），'items'）; 
 $ total_count = $ total_count-> count_all（）; 
  

这是一个可以接受的代码方式吗？
感谢您的帮助。

解决方案

为了不同的目的重用变量是等待发生的维护错误。

这是不好的做法。一个很好的命名变量可以帮助代码理解。

在弱类型的动态语言（如PHP）中，重用变量非常脆弱。

遇到生产代码中的错误（等等，我认为是我的！），其中重用本地循环变量，如i和j导致错误...]

I've looked everywhere, and I can't seem to find an answer one way or another. Is it acceptable (good or bad practice) to reuse or recycle a variable? It works, and I've used this method a few times, but I don't know if I should be doing this or not. I'm trying to get away from using static methods, and moving into dependency injection.

in this example, the $table_name is set elsewhere.

class DbObject {
    private $db = NULL;
    protected $table_name;

    public function __construct($dbh, $item) {
        $this->db = $dbh;
        $this->$table_name = $item;
    }

    // counts items in database //
    public function count_all() {
        try {
            $sql = 'SELECT COUNT(*) FROM ' . $this->table_name;

            $stmt = $this->db->query($sql);
            $stmt->setFetchMode(pdo::FETCH_COLUMN, 0);
            $result = $stmt->fetchColumn();
            return $result;
        } catch (PDOException $e) {
            echo $e->getMessage());
        }
}

To use this I would use it like this:

$total_count = new DbObject(new Database(), 'items');
$total_count = $total_count->count_all();

Is this an acceptable way to code? Thanks for your help.

解决方案

Reusing variables for different purposes is a maintenance error waiting to happen.

It's bad practice. A well named variable can do wonders for aiding code comprehension.

Reusing variables is especially fragile in weakly typed dynamic languages such as PHP.

[In the dim past I have come across errors in production code (wait, I think it was mine!) where reuse of local loop vars like i and j lead to errors...]

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