In English, there's much debate over the "Oxford Comma": in a list of items, do you put a comma between the penultimate item and the "and" before the final one? For example: "The conference featured bad programmers, Remy and TheDailyWTF readers" versus "The conference featured bad programmers, Remy, and the TheDailyWTF readers."

I'd like to introduce a subtly different one: "the concatenator's comma", or if we want to be generic "the concatenator's seperator character", but that doesn't have the same ring to it. If you're planning to list items as a string, you might to something like this pseudocode:

  for each item in items
    result.append(item + ", ")

This naive approach does pose a problem: we'll have an extra comma. So maybe you have to add logic to decide if you're on the first or last item, and insert (or fail to insert) commas as appropriate. Or, maybe isn't a problem- if we're generating JSON, for example, we can just leave the trailing commas. This isn't universally true, of course, but many formats will ignore extra separators. Edit: I was apparently hallucinating when I wrote this; one of the most annoying things about JSON is that you can't do this.

Like, for example, URL query strings, which don't require a "sub-delim" like "&" to have anything following it.

But fortunately for us, no matter what language we're using, there's almost certainly an API that makes it so that we don't have to do string concatenation anyway, so why even bring it up?

Well, because Mike has a co-worker that has read the docs well enough to know that PHP has a substr method, but not well enough to know it has an http_build_query method. Or even an implode method, which handles string concats for you. Instead, they wrote this:

$query = '';
foreach ($postdata as $var => $val) {
$query .= $var .'='. $val .'&';
}
$query = substr($query, 0, -1);

This code exploits a little-observed feature of substr: a negative length reads back from the end. So this lops off that trailing "&", which is both unnecessary and one of the most annoying ways to do this.

Maybe it's not enough to RTFM, as Mike puts it, maybe you need to "RTEFM": read the entire manual.

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