CTFE cannot be used when a struct has "uninitialized" static array union members?

simendsjo simendsjo at gmail.com
Sun Apr 14 05:37:35 PDT 2013


This is probably not a minimal test-case, and I haven't tested 
with more types, but it shows the problem.

// This works
struct S {
     this(int i) {
         a = i;
     }
     union {
         int a = void;
         int b = void;
     }
}
unittest
{
     auto s = S(1);
     assert(&s.a == &s.b);
     enum s2 = S(1);
     static assert(S(1).a == 1);
}

// But this doesn't
struct S2 {
     this(int i) { // error at this line
         a[] = i;
     }
     union {
         int[1] a = void;
         int[1] b = void;
     }
}
unittest
{
     auto s = S2(1);
     assert(s.a.ptr == s.b.ptr);
     // bug.d(19): Error: uninitialized variable 'b' cannot be 
returned from CTFE
     enum s2 = S2(1);
}

void main() {
}


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