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PHP中应该避免使用同名变量(拆分临时变量),php变量
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PHP中应该避免使用同名变量(拆分临时变量),php变量

Jun 13, 2016 am 09:07 AM
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PHP中应该避免使用同名变量(拆分临时变量),php变量

当一个临时变量被赋值多次时,那么将其拆分成多个,除非它是一个循环计数器。

Motivation

临时变量有这多种不同的用途。比如它们可被用作循环中的计数器,在循环中保存结果集,亦或保存一个冗长的表达式的计算结果等等。

这些类型的变量(容器)应该只赋值一次。如果一个同名的临时变量被赋予多个职责,将会影响代码的可读性。这个时候我们应当引入一个新的临时变量以使代码更加清晰易懂。

可能有些注重性能的人会说,引入一个新的变量将会占用更多的内存。的确如此,但是注册一个新的变量不会吸干服务器内存的,这一点请放心,我们不是活在 386 时代,与其在这些无聊的细枝末节上面搞所谓的优化,不如去优化真正的系统性能瓶颈,比如数据库、网络连接等等,而且清晰易懂的代码更容易被重构,发现 Bug,或者解决性能问题等等。

Example Code

很多时候,我们使用同一个 $temp 变量来计算一个物体的不同属性,这种情况比较常见,比如下面这个例子:
复制代码 代码如下:
function rectangle($width=1, $height=1) {
    $temp = 2 * ($width + $height);
    echo "Perimter: $temp
";
 
    $temp = $width * $height;
    echo "Area: $temp";
}

正如你所看到的,$temp 被使用了两次分别用来计算长方形的周长以及面积。这个例子看起来非常直观清晰,但实际的项目代码可能远比这个例子复杂,如果我们把代码改成下面的样子,这样,不管代码如何复杂都不会有混淆感了。

复制代码 代码如下:
function rectangle($width=1, $height=1) {
    $perimeter = 2 * ($width + $height);
    echo "Perimter: $perimeter
";  
 
    $area = $width * $height;
    echo "Area: $area";
}

为不同的东西(如表达式)声明一个新的临时变量吧,大部分时候性能并不是什么问题,而可读性则非常重要。

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