- substr: documentation ( source)
- var_dump: documentation ( source)
- strrpos: documentation ( source)
<?php
$namespaceConstant = "a\\b\\c\\d";
$b = strrpos($namespaceConstant, '\\');
$namespacePart = substr($namespaceConstant, 0, $b);
$constantPart = substr($namespaceConstant, $b);
var_dump($namespacePart);
var_dump($constantPart);