Basic concept for a flexible OOP breadcrumb setup

wp-breadcrumb.php

<?php
interface Wp_Breadcrumb_Strings_Interface {
	public function get_text( $item );
}

class Wp_Breadcrumb_Strings implements Wp_Breadcrumb_Strings_Interface {
	public function get_text( $item ) {}
}


interface Wp_Breadcrumb_Items_Interface {
	public function get_items();
}

class Wp_Breadcrumb_Items implements Wp_Breadcrumb_Items_Interface {
	public function get_items() {}
}


interface Wp_Breadcrumb_Renderer_Interface {
	public function render();
}

class Wp_Breadcrumb_Renderer implements Wp_Breadcrumb_Renderer_Interface {

	private $item_provider;

	private $strings;

	public function __construct(
		Wp_Breadcrumb_Items_Interface    $item_provider,
		Wp_Breadcrumb_Strings_Interface $strings
	) {
		$this->item_provider = $item_provider;
		$this->strings       = $strings;
	}
	public function render() {
		$items = $this->item_provider->get_items();

		if ( empty ( $items ) )
			return;

		foreach ( $items as $item ) {
			$text = $this->strings->get_text( $item );
			// print item
		}
	}
}


function wp_nav_breadcrumb( $args = array() ) {

	$defaults = array (
		'strings'       => 'Wp_Breadcrumb_Strings',
		'item_provider' => 'Wp_Breadcrumb_Items',
		'renderer'      => 'Wp_Breadcrumb_Renderer',
	);

	$classes = wp_parse_args( $args, $defaults );

	$strings = $classes['strings'];

	if ( ! is_object( $strings )
		or ! is_a( $strings, 'Wp_Breadcrumb_Strings_Interface' )
	) {
		$strings = new Wp_Breadcrumb_Strings;
	}

	$item_provider = $classes['item_provider'];

	if ( ! is_object( $item_provider )
		or ! is_a( $item_provider, 'Wp_Breadcrumb_Items_Interface' )
	) {
		$item_provider = new Wp_Breadcrumb_Items;
	}

	$renderer = $classes['renderer'];

	if ( ! is_object( $renderer )
		or ! is_a( $renderer, 'Wp_Breadcrumb_Renderer_Interface' )
	) {
		$renderer = new Wp_Breadcrumb_Renderer( $item_provider, $strings );
	}

	return $renderer->render();
}