WordPress at a glance
function is not described

WC_Email_Customer_Invoice::get_subject() public WC 1.0

Get email subject.

{} It's a method of the class: WC_Email_Customer_Invoice{}

Return

String. Nothing.

Usage

$WC_Email_Customer_Invoice = new WC_Email_Customer_Invoice();
$WC_Email_Customer_Invoice->get_subject();

Code of WC_Email_Customer_Invoice::get_subject() WC 5.3.0

<?php
public function get_subject() {
	if ( $this->object->has_status( array( 'completed', 'processing' ) ) ) {
		$subject = $this->get_option( 'subject_paid', $this->get_default_subject( true ) );

		return apply_filters( 'woocommerce_email_subject_customer_invoice_paid', $this->format_string( $subject ), $this->object, $this );
	}

	$subject = $this->get_option( 'subject', $this->get_default_subject() );
	return apply_filters( 'woocommerce_email_subject_customer_invoice', $this->format_string( $subject ), $this->object, $this );
}