How to shallow copy PHP objects

When assigning, reference assignment is equivalent to taking an alias; modification of one will affect the other. When assigning values ​​in PHP, ordinary objects are deep copied, but objects are shallow copied. In other words, the assignment of an object is a reference assignment. The following introduces the shallow copy of PHP objects. You can refer to it if necessary.

I encountered a low-level bug last week and couldn’t find the problem for a long time. Today when I was squatting in the pit, I didn’t know why this bug came to mind, and then I suddenly realized Check whether it is caused by the object not being cloned.

Sure enough, the problem is that when traversing the same laravel collection multiple times, the properties of the same object are repeatedly operated, causing subsequent operations to overwrite the previous operations, so when the final result is returned, only the The result of the last operation.

Shallow copy

$copy_of_object = clone $object;

Let’s do a test

<?php
class City {
    public $name;
}
$c1 = new City;
$c1->name = "烟台";
echo $c1->name;    // 烟台
echo PHP_EOL;
$c2 = $c1;
echo $c2->name;   // 烟台
echo PHP_EOL;
$c1->name = "威海";
echo $c2->name;   // 威海
echo PHP_EOL;
$c3 = clone $c1;
echo $c3->name;  // 威海
echo PHP_EOL;
$c1->name = "青岛";
echo $c3->name;  // 威海
echo PHP_EOL;

Test results

php /tmp/test.php
烟台
烟台
威海
威海
威海

Why is it called shallow copy?

The corresponding one is deep copy. Because in the case of shallow copy, if the object's attributes are still objects, the attributes still point to the same object.

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