是否有必要在追加之前定义数组？

Question

小问题。

假设我有以下代码

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);

$words = ['Apple', 'Avocado', 'Banana', 'Blueberry'];

$dict = [];
// build a dictionary keyed on the first letter
foreach ($words as $word) {
    $letter = $word[0];
    // is this condition necessary?
    if (!isset($dict[$letter])) {
        $dict[$letter] = [];
    }
    $dict[$letter][] = $word;
}
?>

通常，当我构建字典时，在附加条目之前，我会确保数组存在，如我的示例所示。

我一直以为否则会出现警告，但似乎并非如此。

那么IF条件是否必要？

Answer 1

来自 official documentation on arrays（强调我的）：

$arr[key] = value;

$arr[] = value;

// key may be an integer or string

// value may be any value of any type

If $arr doesn't exist yet, it will be created, so this is also an alternative way to create an array. This practice is however discouraged because if $arr already contains some value (e.g. string from request variable) then this value will stay in the place and [] may actually stand for string access operator. It is always better to initialize a variable by a direct assignment.

不会产生任何警告，但为了清楚起见，最好像您一直在做的那样通过直接赋值进行初始化。

是否有必要在追加之前定义数组？

Is it necessary to define the array before appending to it?

php

multidimensional-array

append

isset