Slices vs Arrays in Carbon language - carbon-lang

Question

What are the differences between Array and Slice in Carbon? I find a document from the official repo. However, it is uncompleted currently.
The following are example codes from the Carbon official repo.
// Carbon:
package Geometry api;
import Math;
class Circle {
var r: f32;
}
fn PrintTotalArea(circles: Slice(Circle)) {
var area: f32 = 0;
for (c: Circle in circles) {
area += Math.Pi * c.r * c.r;
}
Print("Total area: {0}", area);
}
fn Main() -> i32 {
// A dynamically sized array, like `std::vector`.
var circles: Array(Circle) = ({.r = 1.0}, {.r = 2.0});
// Implicitly constructs `Slice` from `Array`.
PrintTotalArea(circles);
return 0;
}
I guess that the Slice is something like std::span, since the C++ version of the codes above uses std::span when the Carbon version uses Slice. Am I correct?
// C++:
#include <math.h>
#include <iostream>
#include <span>
#include <vector>
struct Circle {
float r;
};
void PrintTotalArea(std::span<Circle> circles) {
float area = 0;
for (const Circle& c : circles) {
area += M_PI * c.r * c.r;
}
std::cout << "Total area: " << area << "\n";
}
auto main(int argc, char** argv) -> int {
std::vector<Circle> circles = {{1.0}, {2.0}};
// Implicitly constructors `span` from `vector`.
PrintTotalArea(circles);
return 0;
}

Answer 1

Currently, a first version Arrays exist, while continuing to being worked on, and the Slice type is basically not defined, so it is a bit early to give you a real answer.
As you guessed, it seems like slices might eventually have similarities with std::span, based on some design discussions, but nothing has been approved yet.
You can check the open design proposals on GitHub directly.