致命错误:无法对表达式的结果使用 isset() [英] Fatal error: Cannot use isset() on the result of an expression

问题描述

当使用 isset 编码时，我收到一个致命错误.我已经搜索过 stackoverflow 但结果并不令人满意.

When coding with isset i am getting an fatal error.I have searched stackoverflow but results are not satisfactory.

我得到了

致命错误:不能对表达式的结果使用 isset()(您可以使用null !== expression"代替)

Fatal error: Cannot use isset() on the result of an expression (you can use "null !== expression" instead)

我的代码是

if (!isset( $size || $color )) {
    $style = '';    
}else{
    $style = 'font-size : ' . $size . ';color:' . $color;   
}

推荐答案

如评论(和错误消息)中所述，您不能将表达式的结果传递给 isset.

As mentioned in the comments (and the error message), you cannot pass the result of an expression to isset.

您可以使用多个isset调用，或者反转if/else块的逻辑并将多个参数传递给isset，我认为这是最干净的解决方案:

You can use multiple isset calls, or reverse the logic of your if/else block and pass multiple parameters to isset, which i think is the cleanest solution:

//true if both are set
if(isset($size, $color)) {
    $style = 'font-size : ' . $size . ';color:' . $color;
}else{
    $style = '';
}

您可以通过首先设置默认值来进一步清理它，从而避免需要 else 部分:

You can clean this up a little further by setting the default value first, thus avoiding the need for an else section:

$style = '';
if(isset($size, $color)) {
    $style = 'font-size : ' . $size . ';color:' . $color;
}

您甚至可以使用三元，但有些人发现它们更难阅读:

You could even use a ternary, though some people find them harder to read:

$style = isset($size, $color) ? 'font-size : ' . $size . ';color:' . $color : '';

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