InterfaceInstantiation

An interface is used with new to create an instance. Interfaces cannot be instantiated; only concrete classes that implement the interface can be.

Example

<?php
interface Serializable {
    public function serialize(): string;
}

$obj = new Serializable(); // cannot instantiate interface

How to fix

Instantiate a concrete class that implements the interface instead:

<?php
class JsonSerializable implements Serializable {
    public function serialize(): string {
        return '{}';
    }
}

$obj = new JsonSerializable();