How PHP implements the principle of chain operation

How does PHP implement chain operations? Today I will bring you a detailed explanation of the principle of chain operation in PHP. Share it with everyone and give it as a reference. I hope to be helpful.

There are multiple methods in a class. When you instantiate this class and call the methods, you can only call them one by one, similar to:

db.php

<?php

class db
{
    public function where()
    {
    //code here
    }
    public function order()
    {
    //code here
    }
    public function limit()
    {
    //code here
    }
}

index.php

<?php

$db = new db();

$db->where();
$db->order();
$db->limit();

If you want to implement chain calls, you need to add return $ at the end of the method This is enough.

db.php

<?php

class db
{
    public function where()
    {
    //code here
    return $this;
    }
    public function order()
    {
    //code here
    return $this;
    }
    public function limit()
    {
    //code here
    return $this;
    }
}

index.php

<?php

$db = new db();

$db->where()->order()->limit();

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