how to customize wordpress internal functions, like adjacent_post_link() - wordpress

Question

I need to customize the previous_post_link() and next_post_link() on WordPress.
Per example, I want to shrink permalinks like "Top 5 programming languages that you need to learn" to "Top 5 programing...".
The function responsible for creating the link isadjacent_post_link() located at wp-includes/link-template.php

Answer 1

To create a custom adjacent link for posts I can make use of the filter hook next_post_link and previos_post_link;
In the functions.php:
function shrink_previous_post_link($format, $link){
$in_same_cat = false;
$excluded_categories = '';
$previous = true;
$link='%title';
$format='« %link';
if ( $previous && is_attachment() )
$post = & get_post($GLOBALS['post']->post_parent);
else
$post = get_adjacent_post($in_same_cat, $excluded_categories, $previous);
if ( !$post )
return;
$title = $post->post_title;
if ( empty($post->post_title) )
$title = $previous ? __('Previous Post') : __('Next Post');
$rel = $previous ? 'prev' : 'next';
//Save the original title
$original_title = $title;
//create short title, if needed
if (strlen($title)>40){
$first_part = substr($title, 0, 23);
$last_part = substr($title, -17);
$title = $first_part."...".$last_part;
}
$string = '<a href="'.get_permalink($post).'" rel="'.$rel.'" title="'.$original_title.'">';
$link = str_replace('%title', $title, $link);
$link = $string . $link . '</a>';
$format = str_replace('%link', $link, $format);
echo $format;
}
function shrink_next_post_link($format, $link){
$in_same_cat = false;
$excluded_categories = '';
$previous = false;
$link='%title';
$format='%link »';
if ( $previous && is_attachment() )
$post = & get_post($GLOBALS['post']->post_parent);
else
$post = get_adjacent_post($in_same_cat, $excluded_categories, $previous);
if ( !$post )
return;
$title = $post->post_title;
if ( empty($post->post_title) )
$title = $previous ? __('Previous Post') : __('Next Post');
$rel = $previous ? 'prev' : 'next';
//Save the original title
$original_title = $title;
//create short title, if needed
if (strlen($title)>40){
$first_part = substr($title, 0, 23);
$last_part = substr($title, -17);
$title = $first_part."...".$last_part;
}
$string = '<a href="'.get_permalink($post).'" rel="'.$rel.'" title="'.$original_title.'">';
$link = str_replace('%title', $title, $link);
$link = $string . $link . '</a>';
$format = str_replace('%link', $link, $format);
echo $format;
}
add_filter('next_post_link', 'shrink_next_post_link',10,2);
add_filter('previous_post_link', 'shrink_previous_post_link',10,2);
That all I needed to do. Thanks!

Answer 2

the next_post_link() and previous_post_link() function both come with customization options. http://codex.wordpress.org/Function_Reference/next_post_link. After reading that and learning what the acceptable arguments to the function are, Test to see if it is possible to pass a php function to the option, like substr().
<?php next_post_link('%link',substr('%title',20),FALSE);?>
'%link' and '%title' are shortcodes to the post link and title.
Let us know if it works out.