smarty template variable not clear - php

Question

I am trying to understand developing web apps with PHP and smarty this is the book
there is a file departments_list.tpl
{* departments_list.tpl *}
{load_presentation_object filename="departments_list" assign="obj"}
{* Start departments list *}
<div class="box">
<p class="box-title">Choose a Department</p>
<ul>
{* Loop through the list of departments *}
{section name=i loop=$obj->mDepartments}
{assign var=selected value=""}
{* Verify if the department is selected to decide what CSS style to use *}
{if ($obj->mSelectedDepartment == $obj->mDepartments[i].department_id)}
{assign var=selected value="class=\"selected\""}
{/if}
<li>
{* Generate a link for a new department in the list *}
<a {$selected} href="{$obj->mDepartments[i].link_to_department}">
{$obj->mDepartments[i].name}
</a>
</li>
{/section}
</ul>
</div>
{* End departments list *}
I do not understand in above file one line which is
{section name=i loop=$obj->mDepartments}
how does name=i works I what is i initialized to and how can a loop start from i,
secondly above file is using a file function.load_presentation_object.php
<?php
// Plug-in functions inside plug-in files must be named: smarty_type_name
function smarty_function_load_presentation_object($params, $smarty)
{
require_once PRESENTATION_DIR . $params['filename'] . '.php';
$className = str_replace(' ', '',ucfirst(str_replace('_', ' ',$params['filename'])));
// Create presentation object
$obj = new $className();
if (method_exists($obj, 'init'))
{
$obj->init();
}
// Assign template variable
$smarty->assign($params['assign'], $obj);
}
?>
in above file a parameter $params has been used in last line
$smarty->assign($params['assign'], $obj);
as far as I can understand from file departments_list.tpl passes on parameter to function.load_presentation_object.php
as
{load_presentation_object filename="departments_list" assign="obj"}
so when following is called
function smarty_function_load_presentation_object($params, $smarty)
$params=depratments_list and $smarty=obj
so how does
$smarty->assign($params['assign'], $obj);
work what is $params['assign'] in above?

Answer 1

{load_presentation_object filename="departments_list" assign="obj"}
translated to php will be:
smarty_function_load_presentation_object(
array(
'filename' => 'departments_list',
'assign' => 'obj'
),
$smarty
);
Every parameters specified in smarty template are passed as associative array in first argument. Second is always current smarty object.
As for
{section name=i loop=$obj->mDepartments}
it is simple for loop:
for ($i=0; $i < count($obj->mDepartments); $i++) {
$current = $obj->mDepartments[$i];
}