Why does PHP’s strtotime() not understand a Unix timestamp? Or: Why don’t programming languages support “versions” of themselves? [closed]

Yes, I know that `strtotime` returns a Unix timestamp from a "time string". However, there are numerous situations where I’ve fed a semi-unknown "time string" into it and been baffled when I got a `bool(false)` returned instead of it just returning the same integer back:

``$$current_timestamp = time(); var_dump(strtotime($$current_timestamp)); ``

Output:

``bool(false) ``

I have long since made a wrapper function to `strtotime`, as I have done with every single PHP function I use, which handles this for it, so it’s not a practical problem for me anymore. However, it’s very interesting to me how this kind of situation can happen.

Why do such smart people (no, this is not sarcasm), who are able to create a highly advanced and complex programming language, which I could never do myself even if I got 50 years of "paused time" from now to do it, just seem to "overlook" many such basic "details"?

Is this another case of "we knew about it early on, and agree that it was not right, but people had begun expecting this bad behaviour from the function, and then we couldn’t change it, and as time went by, it became less and less possible"?

I’m very torn about things like this. This particular thing I find idiotic, but there is a good point against changing things around. Just look at the nightmare that is Python. I wouldn’t want to have to constantly try to re-read the manual for every single PHP function I use, wondering if PHP 8.1 or something has changed the parameter order around or something evil like that. If I have to choose between that or fix things myself, I choose the latter.

I just wish that language authors, and in particular PHP since it’s what I use, would just introduce some kind of "legacy mode" where the old/original versions of functions are kept around in the "engine", but only activated unless the user does `<?php8` for their scripts, or something like that. Or maybe set a configuration option, to make the source code files less ugly. That seems like a perfect compromise to me. Why is that not actually done?

Remote APIs, such as Stripe (payment-related), frequently have "versions" where old ones are supported for ages/ever, so why can’t local programming language engines also do that?