php - 数组索引没有按应有的方式执行？

Question

我有以下代码，它让我发疯..

echo $this->year; //This echoes 2019
return $set_year[2019]; //This works, it returns the expected value
return $set_year[$this->year]; //This returns nothing and gives me an 'Undefined Index'

这里发生了什么？这是我设置数组的方式：

return [
    'years' => [

        2019 => 7,
        2018 => 8,
        2017 => 9,
        2016 => 10,
        2015 => 11,
        2014 => 12,
        2013 => 13,

    ],

];

Answer 1

这有效......但我还没有弄清楚为什么

$set_year = Config::get('sitevars.years');
return $this->year ? $set_year[$this->year] : 0;