limpid turtle
The following code doesn't pass the final assert:
pub const TestStruct = union(SmallEnum) {
one: struct { a: u8, b: u32 },
two: struct { b: u32 },
};
pub const SmallEnum = enum(u8) { one, two };
comptime {
std.debug.assert(@sizeOf(TestStruct) == 8);
}
Why is @sizeOf(TestStruct) == 12 when in both union cases there is more than enough space to fit in the SmallEnum tag of u8 size into 8 bytes? Is this a compiler bug?
mortal gull
no, the compiler does not eagerly pack the tag into padding
a tagged union is essentially
struct {
tag: E
data: untagged union {}
}
So there is no way to make a union of size 8 where total bitsize of one of its members is 5 bytes?
mortal gull
bitsize is irrelevant here, the byte size of one's struct is 8 bytes
limpid turtle
Feels then like there should be a way to put inside one struct something like { place_tag_here, a: u8, b:u32} :D. There is no underlaying limitation to prevent this from working. It is simply a Zig language limitation, right?