How to reduce code duplication

Question

As I'm not familiar with PHP I wonde how do I reduce code duplication here? Both methods are doing exactly the same thing here... except the part where the string is extracted (filemtime and basename) and joined.

private function modified_hash( $files ) {
    $joined = "";

    foreach ( $files as $file ) {
        $joined .= filemtime( $file );
    }

    return $this->checksum( $joined );
}

private function filename_hash( $files ) {
    $joined = "";

    foreach ( $files as $file ) {
        $joined .= basename( $file );
    }

    return $this->checksum( $joined );
}

Answer 1

Instead of two functions, declare a unified function with an argument for a crucial callback/function name $func_name:

/**
 * Gets joined files hash
 * 
 * @param $files an array of file paths
 * @param $func_name callback name
 * @return mixed
 */
private function getFilesHash($files, callable $func_name) {
    $joined = "";

    foreach ($files as $file) {
        $joined .= call_user_func($func_name, $file);
    }

    return $this->checksum($joined);
}

Usage:

$fileHash = getFilesHash($files, 'basename');

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Used functions: call_user_func