Just requiring explicit assignment before first use feels like the superior approach to automatic initialization, regardless of whether the automatic initialization is with 0 or with NaN.
The trouble with it is a bug I've seen often. People will get an error message about an "uninitialized variable". Then they go into "just get the compiler to shut up" mode, amd pick "0" as the initializer. Then, the program compiles and runs, and silently produces the wrong answer. Code reviews will simply pass over the "0" initializer, as it looks right.
With default NaN initialization, the programmer is more likely to stop and think about it, not just insert 0.
With the default initialization to nan, do you ever run into situations where people are searching for common sources for nan (nan literals, div by zero) and they can't find it? Or cases where only some branches but not others initialize the float?
To leave a variable uninitialized, use the construction:
int x = void;
Note that nobody is going to write this by accident. And it's easy to grep for.
To find the source of a NaN, it helps to know that every operation that has a NaN as an operand produces a NaN as a result. So if you see a NaN in the output, you can work backwards to where it originated.
> every operation that has a NaN as an operand produces a NaN as a result.
That's not true. The minimum/maximum functions (fmin and fminimum_num variants, but not the fminimum one) treat NaN inputs as not-present, so return the non-NaN value if there is one. Similarly, hypot also treats NaN inputs as not-present. pow and compoundn will ignore NaN exponents if the base is 1.
What do you think of kotlins approach where it has a 'todo' function that can always coerce to a type, but instead of populating the variable with a default value that's valid, it just throws
How long did you think about this before making this declaration? How long did Walter Bright think about this before making his decision when designing his language? Not saying you're wrong, just something to think about perhaps.
C# requires explicit assignment. If an appeal to authority sways you (it shouldn't), you can substitute Anders Hejlsberg instead of this random OP. How long do you suppose Anders Hejlsberg thought about this?
But I contend it's more useful (and interesting) to think about the idea with your own mind instead of tallying up the perceived authority of its supporters and relying on trust. It was also somewhat rude to suggest that the OP had not given their idea much thought. This is a forum for discussion, isn't it?
I think you are misunderstanding what C# does here, and what the original poster was suggesting. Maybe we did a poor job of describing it; I assumed people knew C#. The key words in OP's post were "before first use." It sounds like you interpreted this to mean "every variable declaration must immediately assign a value" but that's not how it works. I'll explain C#'s semantics.
An assignment is required at some point before the first read, not in the declaration. It tracks assignments and usages, and it flags a compiler error if you read a variable before assigning to it for the first time. A variable that hasn't been assigned cannot be read.
It means you can do "int a;" and then later in the function do "a = 5;" and the compiler guarantees that you never read the variable before the assignment in any path through the function. You cannot do "int a;" and then read from it; that's a compile-time error.
It does not mean you have to assign something in the declaration. We never need "vacuous" initializations, and this solution works on all types. Indeed, we avoid vacuous initializations so that the compiler will catch use-before-assign bugs at compile time. The situation you described doesn't happen in C#. Our C# variables become readable on their first assignment, not their declaration; the declaration merely sets the scope. There's no need for a state where it's initialized to an invalid value before receiving the first intended assignment, because in C# the variable is completely inaccessible during that time.
Ok, I understand that. Thank you for the explanation.
An analogous thing happens in D:
int x;
x = 5;
The compiler front end generates two assignments. But then, when it goes through the backend, the first assignment is deleted by what is known as the "dead assignment optimization".
I wasn't really appealing to authority. I was just suspecting a familiar pattern that I always find a little distasteful. Person A describes a brilliant idea they're obviously proud of. Person B casually dismisses it and just claims without evidence that the obvious way of doing it is better. I find that pattern to be not only rude, but to suck some of the joy out of life. The fact that person A on this occasion is widely acknowledged as a brilliant practitioner I thought added weight to me pushing back. But I'd be inclined to feel the same way if person A was an enthusiastic wide eyed student (say) with a fresh perspective.
I can't imagine a situation where that sort of response isn't rude. It's polite to assume people have thought about their opinions, and to address the points rather than the person. If they didn't think it through, then you can counter their points.
In any event, I don't think Walter needed any help here. He is an HN veteran and always willing to discuss the points. Every programming language designer loves an opportunity to discuss their language with interested people! There's almost never a truly right answer in language design, just various tradeoffs.
We're both seeing rudeness. We both dislike rudeness. I think it's rude to rain on someone's parade. You think it's rude to assume someone hadn't thought through their comment (I basically agree) and to address the person rather than the points (I also basically agree).
You might note my original comment included softening elements ("perhaps", "not saying you're wrong"). In general if you look at all my comments you'll see I'm not a rude person, I'm pretty agreeable in general.
I was (trying to) make a meta point rather than a point about the specific technical issue. I agree (again!) that the last word has not been said on this issue or on any other issue where tradeoffs need to be weighed.
I read Walter's comment and thought "Wow, that's a surprising, clever and innovative idea, I'm impressed". And I just didn't enjoy someone bluntly saying, in effect. "No you're wrong, you shouldn't do it like that". It's as simple as that really. I know blunt exchanges of views are normal for programmers and engineers, I don't have to like it every time.
Finally, I know Walter Bright is no shrinking violet and he definitely doesn't need me to defend him!
Sure, but that only matters if default-initialising to NaN significantly reduces them compared to the alternatives. IME it takes a very finely calibrated level of thoughtfulness for your argument in https://news.ycombinator.com/item?id=47928539 to work, to have a programmer who is simultaneously thoughtless enough to initialise to 0 without thinking if the compiler requires initialisation, but thoughtful enough to stop and think about it when the compiler initialises to NaN.
The trouble with it is a bug I've seen often. People will get an error message about an "uninitialized variable". Then they go into "just get the compiler to shut up" mode, amd pick "0" as the initializer. Then, the program compiles and runs, and silently produces the wrong answer. Code reviews will simply pass over the "0" initializer, as it looks right.
With default NaN initialization, the programmer is more likely to stop and think about it, not just insert 0.
Another issue with it is:
For the purposes of code clarity I don't want to see a variable initialized to a value that is never used, just to shut the compiler up.