如何防止在引用更改时更改原始对象？ [重复]

Question

This question already has an answer here:

• How to make a copy of an object without reference? 2 answers

In the following snippet, $sd is a DateTime object. It is assigned to a variable called $a. On calling add on $a, $sd also changes.

$sd = new DateTime();
$a = $sd;
$a->add(new DateInterval("P1M")); // Add 1 month to $a

This happens because $a was a reference to $sd. Is there a way, where $sd doesn't change? What should be the approach here?

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Answer 1

Use clone

$sd = new DateTime();
$a = clone $sd;
$a->add(new DateInterval("P1M")); // Add 1 month to $a