array_merge() 和 運(yùn)算符在合并數(shù)組時(shí)的關(guān)鍵區(qū)別在于鍵的處理和值的覆蓋方式。1. array_merge() 會(huì)重新索引數(shù)字鍵并保留字符串鍵，后續(xù)數(shù)組中的同名鍵值會(huì)覆蓋前面的；2. 運(yùn)算符則保留所有鍵，遇到鍵沖突時(shí)保留左側(cè)數(shù)組的值，右側(cè)數(shù)組的值被忽略。因此，若需允許覆蓋且不介意數(shù)字鍵被重排，使用 array_merge()；若需保留原始鍵值且避免覆蓋，則使用 運(yùn)算符。

In PHP, both array_merge() and the operator are used to combine arrays, but they behave quite differently — especially when dealing with overlapping keys. Here's how they differ and when you might want to use each one.

How array_merge() works

When you use array_merge(), PHP combines arrays and reindexes numeric keys starting from zero, while preserving string keys. If there are overlapping keys (especially string keys), the later array's value will overwrite the earlier one.

Example:

$a = ['a' => 1, 'b' => 2];
$b = ['b' => 3, 'c' => 4];
$result = array_merge($a, $b);
// Result: ['a' => 1, 'b' => 3, 'c' => 4]

• Numeric keys get reindexed.
• String keys are preserved.
• Duplicate string keys in later arrays replace earlier ones.

Use this when:

• You want to merge arrays and allow overwriting of duplicate keys.
• You’re okay with numeric keys being renumbered.

How the operator works

The operator merges two or more arrays by preserving all keys, and if there’s a key collision, the value from the leftmost array wins — meaning duplicates in the right-hand array are ignored.

Example:

$a = ['a' => 1, 'b' => 2];
$b = ['b' => 3, 'c' => 4];
$result = $a   $b;
// Result: ['a' => 1, 'b' => 2, 'c' => 4]

• Keys are not reindexed (both numeric and string).
• In case of key conflicts, the first occurrence is kept.
• The order matters — left side takes priority.

Use this when:

• You want to preserve all original values, even if there are duplicates.
• You need to "fallback" data from another array without overriding existing keys.

Key differences summarized

Here's a quick breakdown:

• Key handling:

  • array_merge() reindexes numeric keys and replaces duplicate string keys.
  • keeps all keys intact and retains the first encountered value for duplicates.

• Overwrite behavior:

  • array_merge() lets newer values overwrite older ones.
  • sticks with the first value and ignores new ones.

• Return type:

  • Both return a new array and don't modify the originals.

So depending on whether you care about preserving keys or allowing overwrites, you'll pick one or the other.

基本上就這些。

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