Error "No database selected" When initializing a class's properties by returning a reference to a function

php
  
   connect_error) {        die("Connection failed: " . $conn->connect_error);    }    $conn->query("SET NAMES 'UTF8'");    return $conn;}?>

php
  
   conn=connectdb();        $result=$this->conn->query("SELECT * FROM 15_spring_new WHERE 1;");        var_dump($this->conn->error);    }}$bar = new Bar; ?>

This problem occurs whenever a call is found in a function.
The error output is: "No database Selected"
And when I use outside of the class, the program runs normally.
Where is the error?

Reply content:

php
  
   connect_error) {        die("Connection failed: " . $conn->connect_error);    }    $conn->query("SET NAMES 'UTF8'");    return $conn;}?>

php
  
   conn=connectdb();        $result=$this->conn->query("SELECT * FROM 15_spring_new WHERE 1;");        var_dump($this->conn->error);    }}$bar = new Bar; ?>

This problem occurs whenever a call is found in a function.
The error output is: "No database Selected"
And when I use outside of the class, the program runs normally.
Where is the error?

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