Traps to Developers

projects that do this drive me bananas

If I had the emotional energy, I'd open a JEP for a new @java.lang.NonNullReference and any type annotated with it would be a compiler error to assign null to it

  public interface Alpha {}
  @java.lang.NonNullReference
  public interface Beta {}

  Alpha a = null; // ok
  Beta b = null; // compiler error

  Beta b;
  if (Random.randBoolean()) {
    b = getBeta();
  } else {
    b = newBeta();
  }

  Beta b;
  if (true) {
    b = getBeta();
  } else {
    b = null; // I believe this will be elided and thus technically legal
  }

That’s incorrect for Java, possibly also for C# and JS.

In any language where strings are opaque enough types [1], the in-memory representation is an implementation detail. Java has been such a language since release 9 (https://openjdk.org/jeps/254)

[1] The ‘enough’ is because some languages have fully opaque types, but specify efficiency of some operations and through it, effectively proscribe implementation details. Having a foreign function interface also often means implementation details cannot be changed because doing that would break backwards compatibility.

> JS use floating point for all numbers. The max accurate integer is 2⁵³−1

That is incorrect. Much larger integers can be represented exactly, for example 2¹⁰⁰.

What is true is that 2⁵³−1 is the largest integer n such that n-1, n, and n+1 can be represented exactly in an IEEE double. That, in turn, means n == n-1 and n == n+1 both will evaluate to false, as expected in ‘normal’ arithmetic.

Once a TCP connection has been established there is no state on routers in between the 2 ends of the connection. The issue here is firewalls / NAT entries timing out. And indeed, no RSTs are sent.

We had the issue in K8s with the conntrack module set too low.

Now, you can try to put in an HTTP Keep-Alive, but that will not help you. The HTTP Keep-Alive is merely for connection re-use at the HTTP level, i.e. it doesn't close the connection: https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/...

An HTTP Keep-Alive does not generate any packages, it merely postpones the close.

A TCP Keep-Alive generates packages which resets the timers.

I wonder if anyone can learn from this. I feel like I only understood what I already knew, or at least was very close to knowing. That's the same thing that happens with teaching manuals about any topic: they're organized in a way that makes sense and it's easy for people who already know the topics, but often very bad at teaching the same topics to an audience that doesn't know anything.

Much of it would only apply in certain relatively narrow contexts, but the contexts aren't necessarily mentioned.

Some of it appears to be just wrong.

I guess I'm saying: I would not take this literally, but as something almost like a stream-of-consciousness.

> Unicode unification. Different characters in different language use the same code point. Different languages' font variants render the same code point differently. 語

This isn't a trap. The given example character means the same thing in Chinese and Japanese, and the Japanese version was imported from China. People from both languages recognize both font variants as the same conceptual character.

The author is making it sound like the letter 'A' in English should have a different code point than an 'A' in French. Or that a lowercase 'a' with the top tail should be a different character than a lowercase 'a' without the top tail.

Anyway, this is discussed at length in https://en.wikipedia.org/wiki/Han_unification

> There is a negative zero -0.0 which is different to normal zero. The negative zero equals zero when using floating point comparision. Normal zero is treated as "positive zero".

And there are two ways to distinguish negative zero from normal zero: By their integer bit patterns, or by the fact that 1.0/-0.0 == -Inf vs. 1.0/0.0 == +Inf.

> It's recommended to configure the server's time zone as UTC.

Big yes. I use UTC for servers, logs, photos, and anything that is worth archiving and timestamping properly. Local time is only for colloquial use.

> For integer (low + high) / 2 may overflow. A safer way is low + (high - low) / 2

Yes, but if low and high could be negative numbers, then you've just shifted the overflow to a different range. This matters for general binary search over an integer range, as opposed to unsigned binary search over an array.

> C/C++

I'm going to throw in one of my lists of pitfalls - just using integer types and arithmetic correctly in C/C++ is a massive developer trap. That's like the most basic thing in programming. https://www.nayuki.io/page/summary-of-c-cpp-integer-rules

> Rebase can rewrite history

"Can" is a weasel word; rebase does nothing but rewrite history.

From MDN: "For block boxes, inline boxes, inline blocks, and all table layout boxes auto resolves to 0."

https://developer.mozilla.org/en-US/docs/Web/CSS/min-width

"There is no guarantee of a single total ordering of volatile writes as seen from all threads of execution"

https://learn.microsoft.com/en-us/dotnet/csharp/language-ref...

Regex semantics is subtly different across languages. E.g. a{,3} matches between 0 and 3 "a" characters in Python. In JavaScript it matches the literal string "a{,3}".

I've write tons and tons of CSS, have done for a decade. I don't sit and think about the exact interactions, I just know a couple things that might work if I'm getting something unexpected.

I don't really see it possible to commit that to memory, unless I literally start working on an interpreter myself.

sweet mercy :O

Someone call the Inquisition

Nope. It’s just bytes with no encoding.

https://go.dev/blog/strings