Advent of Code 2023

[Siarhei Siamashka]

On Sunday, 3 December 2023 at 18:56:32 UTC, Johannes Miesenhardt 
wrote:
> On Sunday, 3 December 2023 at 14:51:37 UTC, Siarhei Siamashka 
> wrote:
>> [...]
>
> Thanks, this is super helpful. I have one other question, in 
> the solution you posted and also the one I posted in the 
> discord today. I was required to use byLineCopy. I first used 
> byLine but I for some reason that I can't really explain only 
> got the last line from that. I switched to byLineCopy because I 
> saw it in other peoples solution and that magically fixed all 
> problems I had. What exactly happened here?

It's very important to know how slices and garbage collector work 
together in D language. In particular, the results produced by 
the following code may look surprising to beginners:

```D
import std;

void f1(ref int[] x) {
   x[0] += 1;
   x    ~= [9, 9, 9, 9, 9, 9];
   x[0] -= 1;
}

void f2(int[] x) {
   x[0] += 1;
   x    ~= [9, 9, 9, 9, 9, 9];
   x[0] -= 1;
}

void main() {
   int[] a = [1, 2, 3, 4];
   writefln!"original:       %s"(a); // [1, 2, 3, 4]
   f1(a);
   writefln!"after f1:       %s"(a); // [1, 2, 3, 4, 9, 9, 9, 9, 
9, 9]
   f2(a);
   writefln!"after f2:       %s"(a); // [2, 2, 3, 4, 9, 9, 9, 9, 
9, 9]
   f2(a);
   writefln!"after f2 again: %s"(a); // [3, 2, 3, 4, 9, 9, 9, 9, 
9, 9]
   a.reserve(100);
   writefln!"reserved extra capacity to allow doing resize 
in-place";
   f2(a);
   writefln!"after f2 again: %s"(a); // [3, 2, 3, 4, 9, 9, 9, 9, 
9, 9]
}

```

Coming from the other programming languages, people are usually 
familiar with the concept of passing function arguments either by 
value or by reference. And the behavior of the `f2` function may 
seem odd in the example above. It never changes the size of the 
original array, but may modify its data in unexpected ways 
contrary to naive expectations. There's a detailed article on 
this topic, where all the necessary answers can be found: 
https://dlang.org/articles/d-array-article.html

Many functions in D language have their pairs/siblings. The 
potentially wasteful `.byLineCopy` has its potentially 
destructive sibling `.byLine`. There are also 
`.split`/`.splitter` or `.retro`/`.reverse` pairs with their own 
subtle, but important differences. The beginners may prefer to 
start with the less efficient, but easier to use variants with no 
undesirable side effects.