Split string by delimiter, but not if it is escaped

Question

How can I split a string by a delimiter, but not if it is escaped? For example, I have a string:

1|2\\|2|3\\\\|4\\\\\\|4

The delimiter is <

Answer 1

Regex is painfully slow. A better method is removing escaped characters from the string prior to splitting then putting them back in:

$foo = 'a,b|,c,d||,e';

function splitEscaped($str, $delimiter,$escapeChar = '\\') {
    //Just some temporary strings to use as markers that will not appear in the original string
    $double = "\0\0\0_doub";
    $escaped = "\0\0\0_esc";
    $str = str_replace($escapeChar . $escapeChar, $double, $str);
    $str = str_replace($escapeChar . $delimiter, $escaped, $str);

    $split = explode($delimiter, $str);
    foreach ($split as &$val) $val = str_replace([$double, $escaped], [$escapeChar, $delimiter], $val);
    return $split;
}

print_r(splitEscaped($foo, ',', '|'));

which splits on ',' but not if escaped with "|". It also supports double escaping so "||" becomes a single "|" after the split happens:

Array ( [0] => a [1] => b,c [2] => d| [3] => e )