On 4/22/21 6:47 PM, Rekel wrote:
I'm not sure why this is happening, but after simplifying my code I
traced it back to what the title may suggest. The original cause of my
issues being summarized by debug print statements returning a union as:
Mat([nanf, nanF, . . . .], [[1.0F, 0.0F, . . . .])
Even though the nanF should thus be 1.0, 0.0, etc...
This is example code that describes when this happens:
```d
import std.stdio;
struct Apple(uint size) {
union {
int[size * size] a;
int[size][size] b;
}
static immutable typeof(this) pie = _pie();
private static typeof(this) _pie() pure {
typeof(this) result;
static foreach (i; 0 .. size)
static foreach (j; 0 .. size)
//result.a[i + j * size] = 1; // Works
result.b[i][j] = 1; // Fails
return result;
}
}
void main() {
Apple!(4) a = Apple!(4).pie;
writeln(a.a);
writeln(a.b);
}
```
The working code changes the first integers to 1, the failing version
keeps them at 0.
What's the reason for this? Logically this doesn't seem troublesome to
me, and if assigning to non-initial anonymous union varialbes isn't
possible(?!) that would be pretty bad, and I'd be in for quite some
trouble in my actual code :(
I think this is a bug. For sure, the only 2 valid options are, it should
compile and do what you are expecting, or not compile.
CTFE unions are (I think) implemented as a "tagged" union, where only
one value is set. When you assign to a *part* of b, you are assigning to
something that isn't being used.
Normally, in CTFE, using a union member that isn't set is an error
(compile-time because CTFE).
If you assign to b all at once, it works:
```d
private static typeof(this) _pie() pure {
typeof(this) result;
typeof(b) val;
static foreach (i; 0 .. size)
static foreach (j; 0 .. size)
val[i][j] = 1;
result.b = val;
return result;
}
```
I think the compiler is allowing the usage of a part of b without the
tag being updated. Probably the right answer is, setting an element of b
should be an error, or it should switch the tag (if the union was never
set).
BTW, I think the fact that the union members are arrays is important.
Please file a bug.
-Steve
