What are some easy-to-solve errors you spent awhile fixing?

When cd drives first came out I got one and then wrote my own program in assembly to display all the information about the drive and disc that you normally can't see (because it was just drive E: or whatever to DOS/Windows).

I named the program cd. It took me way too long to figure out my mistake.

I had an issue with a balanced binary tree. At some point, it would bomb out when adding another node.

It took me ages to recognize that at one point of the balancing algorithm, instead of

if (something) {
    [...]
} else {
    [...]
}

I had written

if (something) {
    [...]
} {
    [...]
}

I once spent three days , 30 hours, because I was writing text with new lines as a binary stream.

4 keystrokes to fix

Not sure if this question is too noobish for !programming@programming.dev so I posted it here just in case.

I spent three days trying to get a RaycastCommand (Unity's jobified raycasts) working to get multiple hits per raycast. Should have been easy, according to the docs:

The result for a command at index N in the command buffer will be stored at index N * maxHits in the results buffer.

If maxHits is larger than the actual number of results for the command the result buffer will contain some invalid results which did not hit anything. The first invalid result is identified by the collider being null

maxHits The maximum number of Colliders the ray can hit

Well, no. I was getting super weird results and couldn't get it to work properly. First thing I checked was if I'm getting to hits for any of the raycasts, because you simply can't trust Unity. And I was getting multi hits, but seemingly at random.

The error? I was sorting the hits by distance using bubblesort, and made a simple error with index in it. Which resulted in me seemingly getting two hits per ray sometimes, but it was just a result for another ray moved there by faulty bubblesort. Because unity actually doesn't support multiple hits per ray.

I couldn't find the original thread about the issue (which was two years old by the time I was dealing with it), which had an amazing reply from Unity:

I have discussed it with an engineering team, and RaycastCommands don't support multiple hits because it was difficult to implement. The documentation just doesn't explains it really well

The fuck doesn't explain it very well??? It literally describes a parameter that sets max hits per ray and tells you how to get the multi hits from results...

Fuck unity :D

My top 3 (as mainly JS dev) would be:

1. Number overflow. It happens when you're backend send big number ID serialized in a JSON. The solution is to wrap the number into a string when you know that can happens.

JSON.parse('{"n": 123456789123456789012.0}').n
// => 123456789123456800000

2. Mutating an Object by ref (now I use Object.freeze a lot). Something like:

const CONFIGURATION = { conf: { enabled: false } }
// setup a "copy"
let currentConfiguration = { ...CONFIGURATION }
currentConfiguration.conf.enabled  = true
// try to reset the conf
currentConfiguration = { ...CONFIGURATION }
// => { conf: { enabled: true } }

3. Assignation instead of comparison (now my IDE warn me)

if (foo = false) {
  // do something
}

That's one of the things I really like about ruby. You can use p blah instead of puts blah and it will output the actual object structure rather than just the string impl. So for example:

❯ irb
irb(main):001:0> blah = " abcd "
=> " abcd "
irb(main):002:0> puts blah
 abcd
=> nil
irb(main):003:0> p blah
" abcd "
=> " abcd "
irb(main):004:0>

(p just calls puts blah.inspect, where .inspect is a method implemented on many default objects)