WP_User::set_role() WordPress Method

	public function set_role( $role ) {
		if ( 1 === count( $this->roles ) && current( $this->roles ) == $role ) {
			return;
		}

		foreach ( (array) $this->roles as $oldrole ) {
			unset( $this->caps[ $oldrole ] );
		}

		$old_roles = $this->roles;

		if ( ! empty( $role ) ) {
			$this->caps[ $role ] = true;
			$this->roles         = array( $role => true );
		} else {
			$this->roles = array();
		}

		update_user_meta( $this->ID, $this->cap_key, $this->caps );
		$this->get_role_caps();
		$this->update_user_level_from_caps();

		foreach ( $old_roles as $old_role ) {
			if ( ! $old_role || $old_role === $role ) {
				continue;
			}

			/** This action is documented in wp-includes/class-wp-user.php */
			do_action( 'remove_user_role', $this->ID, $old_role );
		}

		if ( $role && ! in_array( $role, $old_roles, true ) ) {
			/** This action is documented in wp-includes/class-wp-user.php */
			do_action( 'add_user_role', $this->ID, $role );
		}

		/**
		 * Fires after the user's role has changed.
		 *
		 * @since 2.9.0
		 * @since 3.6.0 Added $old_roles to include an array of the user's previous roles.
		 *
		 * @param int      $user_id   The user ID.
		 * @param string   $role      The new role.
		 * @param string[] $old_roles An array of the user's previous roles.
		 */
		do_action( 'set_user_role', $this->ID, $role, $old_roles );
	}