Is there any way to check if an element has been initialized?

[worn pier]

Suppose I have a slice of a type that requires to be initiallized. The slice is created as:

var arr: []T = allocator.alloc(T, 10);

for some type T with the above restriction and some allocator. Is there any way to check if, for instance, arr[1] has been initialized?

For context, I want to know in a function, if a certain element has been initiallized, because if it has, I need to call the set funciton of that element, but if it has not, I need to create a new object of that type:

arr[1] = T{ .somedata = "foo" };

[flat roost]

its not possible
youd need to use a different way to keep track of what is initialized or just use optionals

const arr = allocator.alloc(?T, 10);
@memset(arr, null);
// later
for (arr) |*maybe_e| {
  if (maybe_e) |*e| {
    e.set()
  } else {
    e.* = .{ .somedata = "foo" };
  }
}

[regal turret]

you can have a metadata field in T, can be more space efficient than optional.

[flat roost]

depends on how T is laid out but yeah

although ideally youd just store it out of band
where you have an array of uninitialized Ts that get popped and initialized before going into the array of initialized Ts

if thats possible

[regal turret]

An optional type (tagged union a.k.a. enum + union) will have nice alignment in memory so will not be packed to smallest memory, which is good for performance. But a metadata field can be handy since you can let the first bit be the empty/exist bool, then store some other information about T in the other bits . And if T would be a packed struct from the start, a metadata field is your best option I would think.

[flat roost]

will have nice alignment in memory
everything but a packed struct will have each field aligned, so thats a moot point

basically any time you have padding, you can afford a is_optional field

[regal turret]

^ yea

[flat roost]

either way, optionals will never be smaller than just the sturct + a bool