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.
