Wordpress - Passing a variable to get_template_part

As posts get their data set up via the_post() (respectively via setup_postdata()) and are therefore accessible through the API (get_the_ID() for e.g.), let's assume that we are looping through a set of users (as setup_userdata() fills the global variables of the currently logged in user and isn't useful for this task) and try to display meta data per user:

<?php
get_header();

// etc.

// In the main template file
$users = new \WP_User_Query( [ ... ] );

foreach ( $users as $user )
{
    set_query_var( 'user_id', absint( $user->ID ) );
    get_template_part( 'template-parts/user', 'contact_methods' );
}

Then, in our wpse-theme/template-parts/user-contact_methods.php file, we need to access the users ID:

<?php
/** @var int $user_id */
$some_meta = get_the_author_meta( 'some_meta', $user_id );
var_dump( $some_meta );

That's it.

Update (WP >= v5.5)

As pointed out in the comments, current versions of WP offer a third parameter for [get_template_part()][1]: array $args. So from this version on, you do not need to use set_query_var( 'foo', 'bar' ) anymore. Example:

<?php
get_header();

// etc.

// In the main template file
$users = new \WP_User_Query( [ ... ] );

foreach ( $users as $user )
{
    $args = (array) $user;
    get_template_part( 'template-parts/user', 'contact_methods', $args );
}

Then, in our wpse-theme/template-parts/user-contact_methods.php file, we need to access the users ID:

<?php
/** @var array $args */
$some_meta = get_the_author_meta( 'some_meta', $args['ID'] );
var_dump( $some_meta );

---

The explanation is actually exactly above the part you quoted in your question:

However, load_template(), which is called indirectly by get_template_part() extracts all of the WP_Query query variables, into the scope of the loaded template.

The native PHP extract() function "extracts" the variables (the global $wp_query->query_vars property) and puts every part into its own variable which has exactly the same name as the key. In other words:

set_query_var( 'foo', 'bar' );

$GLOBALS['wp_query'] (object)
    -> query_vars (array)
        foo => bar (string 3)

extract( $wp_query->query_vars );

var_dump( $foo );
// Result:
(string 3) 'bar'

The hm_get_template_part function by humanmade is extremely good at this and I use it all the time.

You call

hm_get_template_part( 'template_path', [ 'option' => 'value' ] );

and then inside your template, you use

$template_args['option'];

to return the value. It does caching and everything, though you can take that out if you like.

You can even return the rendered template as a string by passing 'return' => true into the key/value array.

/**
 * Like get_template_part() put lets you pass args to the template file
 * Args are available in the tempalte as $template_args array
 * @param string filepart
 * @param mixed wp_args style argument list
 */
function hm_get_template_part( $file, $template_args = array(), $cache_args = array() ) {
    $template_args = wp_parse_args( $template_args );
    $cache_args = wp_parse_args( $cache_args );
    if ( $cache_args ) {
        foreach ( $template_args as $key => $value ) {
            if ( is_scalar( $value ) || is_array( $value ) ) {
                $cache_args[$key] = $value;
            } else if ( is_object( $value ) && method_exists( $value, 'get_id' ) ) {
                $cache_args[$key] = call_user_method( 'get_id', $value );
            }
        }
        if ( ( $cache = wp_cache_get( $file, serialize( $cache_args ) ) ) !== false ) {
            if ( ! empty( $template_args['return'] ) )
                return $cache;
            echo $cache;
            return;
        }
    }
    $file_handle = $file;
    do_action( 'start_operation', 'hm_template_part::' . $file_handle );
    if ( file_exists( get_stylesheet_directory() . '/' . $file . '.php' ) )
        $file = get_stylesheet_directory() . '/' . $file . '.php';
    elseif ( file_exists( get_template_directory() . '/' . $file . '.php' ) )
        $file = get_template_directory() . '/' . $file . '.php';
    ob_start();
    $return = require( $file );
    $data = ob_get_clean();
    do_action( 'end_operation', 'hm_template_part::' . $file_handle );
    if ( $cache_args ) {
        wp_cache_set( $file, $data, serialize( $cache_args ), 3600 );
    }
    if ( ! empty( $template_args['return'] ) )
        if ( $return === false )
            return false;
        else
            return $data;
    echo $data;
}

I was looking around and have found a variety of answers. Its seems at a native level, Wordpress does allow for variables to be accessed in Template parts. I did find that using the include coupled with locate_template did allow for variables scope to be accessible in the file.

include(locate_template('your-template-name.php'));