4 ms·

The Nil-Coalescing Operator they add is actually redundant. Instead of their new fancy syntax: print(message ?? "The message was nil.") The idiomatic way w

• DemocracyFTW2 3y ago
  No it's not the same; `x ?? 'foo'` evaluates to `x` when `x` is not `nil` and to `'foo'` otherwise; `x or 'foo'` evaluates to `x` when `x` is not one of `nil` or `false`, and to `'foo'` otherwise. This idiom seems to have been made widely popular by Perl folks, and while it has always been a good trick up your sleeve when you're 16 and want to impress the other kids, it's never been a good, correct way of doing things seriously, especially not across different scripting languages when every single one has its own Byzantine rules of what counts as truthy and what as falsey (like empty strings or empty lists). It is an especially pernicious idiom because of the widespread clout with which it tends to be transmitted; turns out it's one of the Falsehoods Clever Programmers Think They Know Better About. They don't.
  • ledauphin 3y ago
    i can see you are probably a polyglot, working in several languages with regularity. it would certainly be frustrating to have to juggle these semantics as you switched back and forth. however, languages are just that - they have their own meanings, and unfortunately they can't all be the same across languages (or they'd all be the same language).
    • DemocracyFTW2 3y ago
      different languages are different, and they have every right to be different, and I have every right to point out in whichever ways they differ. Personal tastes differ, too, and as far as I'm concerned I think that using 'shorthand Boolean coalescence' (I just made up that term) is a false convenience; when I write a condition that relies on a list being empty, ideally that should look like `if is_empty a then ...` according to my taste—explicit is better than implicit, and this is still concise. Be that as it may but shrugging and sighing, like, "ah well, different languages will be different" and using that as an argument against a discussion of the merits and demerits of certain aspects of certain languages is not constructive, is it?
  • naniwaduni 3y ago
    You want to learn the specifics of ?? means in this language, but not the boolean projections? It's one thing to be peeved that empty strings or lists are falsy when it's useful for them not to be, but this seems like barking up the wrong tree.
    • fieldcny 3y ago
      I’m not clear on what the point of your response is, the comment you responded to is making an often overlooked point that certain subtleties in how languages implement constructs can create sharp edges, one of those being the null coalescing operator.
      • smegsicle 3y ago
        the point is that lua didn't make the mistake of false 'empty' values, so that particular sharp edge is absent
        • DemocracyFTW2 3y ago
          The edge of "false 'empty' values" is absent in Lua, indeed, but the `a = b or c`, more often used in the form `b = b or c`, has, in Lua, still the problem that it will evaluate to `c` if `b` is `nil` and when b is `false` which may or may not be what one wants—and often one wants it not. The idiom is commonly used to assign a proper value to a variable that has not been set to an explicit value, i.e. a variable that is `nil`. The assignment `b = b or true` will set `b` to `true` if it was `nil` or `false`; assuming allowable values for `b` are `true` and `false` and the default is `true`, `b` will then never keep the value of `false` and always be set to `true`.
    • DemocracyFTW2 3y ago
      You almost never want to exploit, in a scripting language, the subtleties of the Boolean projections when writing the (un-) idiom `b = b or b_default`; it is more commonly a mistake made by script kiddies and hand-waving mavericks (i.e. People Who Finish First, a.k.a. People Who Never Write Proper Tests) that has become deeply ingrained due to the Look Ma How Clever effect. If `b` should be a Boolean with a default of `true` then `b = b or true` will quite obviously never allow it to be `false`. Rewrite that and put it in a row of such assignments as in `a = a or a_default; b = b or b_default`; c or c or c_default;` and it looses its fishy smell enough to pass as "OK, trivially no problem here". I've indeed gotten tired by the entire idea of Boolean projections, yes, but that's not the point here, at least not almost always in practice.
  • cardanome 3y ago
    Empty strings, lists and the number 0 are all truthy in Lua so this isn't an issue. Different languages have different semantics. Yes, using the or operator like that is not a good idea in many languages but in Lua it is idiomatic.
    • DemocracyFTW2 3y ago
      pls see my other comment(s)
  • awwaiid 3y ago
    Well the Perl people also invented the defined-or operator (//), so there is that.
    • DemocracyFTW2 3y ago
      I was just guessing here and didn't know about `//`; this in turn comes transparently from C as an enhancement of the C idiom `b = b || c`; it may have been a later introduction though (me learning Perl was way back in the (early?) 90s) or I missed it (not unlikely)
• deleted 3y ago
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• wk_end 3y ago
  It’s been too long since I’ve played with Lua to recall whether this would also be the case, but in JS the nullish coalescing operator is useful over logical OR because it prevents false-y values (0, empty string, false) from being treated as nullish ones, a frequent source of bugs.
  • cardanome 3y ago
    The number 0 and empty strings are considered truthy, so it isn't that bad. return 0 or 42 > 0 Obviously the pattern doesn't work for checking for the existence of booleans as both nil and false are falsy but you are less likely to confuse that. So yes, the ?? would help a little bit but then again, you could just explicitly check for nil.
    • adbachman 3y ago
      > the ?? would help a little bit that's the only point of the operator. given: a = 0; b = 42; then `a or b` and `a ?? b` give two different answers, but take the same number of characters to write. > just explicitly check for nil 1. I am lazy and 2. I am explicitly checking, that's why I picked `??` not `or`
  • smegsicle 3y ago
    false-y values in dynamically typed languages is a mistake
    • nine_k 3y ago
      Coming from Python, I find empty collections being falsey very convenient.
      • durumu 3y ago
        I feel like typing len(...) is not that bad, compared to how verbose "default if var_to_test is None else var_to_test" is (compared to "var_to_test or default"). But I agree it is nice -- I wish Python had the ?? operator.
• tvb12 3y ago
  Even though it would make the language a little more verbose, I would love if Lua had a 'global' keyword and declaring global/local was required. With that one change, I think Lua would have the best implementation of scope out of any language I've used.
  • thefaux 3y ago
    Yes. My solution though is to just pretend that naked assignment isn't supported and don't use global variables.
• nmz 3y ago
  Penlight[1] was supposed to offer python like batteries. It's kind of been abandoned by now, as has most of lua IMV. To me you still need luastd and a couple of other things (posix, lfs, socket, luasec) you can just fetch with luarocks and you're semi set. [1]: https://lunarmodules.github.io/Penlight/ https://lunarmodules.github.io/Penlight/
• trynumber9 3y ago
  It is actually not redundant. I have run into this problem at least once in real Lua code. local x = false print(x ?? "message was nil") print(x or "message was nil") which results in >false >message was nil