backtrace(); Safely return current backtrace as array of formatted strings

backtrace.php

<?php

/**
 * Returns an array of formatted backtrace lines.
 * Optional format string may include the following keywords:
 *  index       Zero-based order number of backtrace step.
 *  file        Path and name of file
 *  line        Line number
 *  class       Fully qualified name of class
 *  type        `::` if class method or `->` if object method
 *  function    Name of the method or function
 * 
 * The call to the backtrace function is always skipped. 
 * Additional calls may be skipped using the `$skip` parameter.
 * 
 * @param string|null $format Default `'#index file(line): classtypefunction(?)'`
 * @param int         $skip
 *
 * @return string[]
 */
function backtrace(string $format = null, int $skip = 0) : array
{
    $format = $format ?: '#index file(line): classtypefunction(?)';

    $trace = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS);

    array_splice($trace, 0, $skip + 1);

    return array_map(function ($step, $index) use ($format) {
        $step['index'] = $index;
        return strtr($format, $step);
    }, $trace, range(0, count($trace)));
}

Note; formatting of function calls untested. Should look fine, as it's just replaced with empty strings.

Default format based on Exception::getTraceAsString() minus the arguments.