What is the difference between passing by value and reference in php?

Passing value

Passing value is to copy the value of the variable to a new value (the value is the same), There are just two different memory spaces in the memory. Assign the new value memory space address to the new variable name. Modifying the values ​​of the two variables has no effect.

$a1 = 234;
$a2 = 34556;
$a1 = $a2;
var_dump($a1,$a2);
$a2 = 'nongjiale.fun';
var_dump($a1,$a2);

Reference

Reference is to copy the reference of the variable (the new reference still points to the original value).

$y1 = 23;
$y2 = 433;
var_dump($y1,$y2);//输出int 23 int 433
$y2 = &$y1;
$y2 = 'mudidi.tech';
var_dump($y1,$y2);//输出string 'mudidi.tech' string 'mudidi.tech'

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