Bug 19079 – Destructors not called in named unions

When a type T with a destructor is placed in a named union, T's destructor is not called when the union goes out of scope or is destroyed with destroy(). https://dlang.org/spec/struct.html states that 'Unions may not have fields that have destructors', so this may be undefined behavior. struct S { ~this() { throw new Exception(""); } } struct S1 { union { S s; } } union U { S s; } struct S2 { U u; } unittest { import std.exception; // Correct behavior: assertThrown((){ S s; }()); assertThrown((){ S s; destroy(s); }()); assertThrown((){ S1 s1; }()); assertThrown((){ S1 s1; destroy(s1); }()); // Incorrect behavior: assertNotThrown((){ U u; }()); assertNotThrown((){ U u; destroy(u); }()); assertNotThrown((){ S2 s2; }()); assertNotThrown((){ S2 s2; destroy(s2); }()); }

As mentioned in issue 19122, and quoting from https://github.com/dlang/dmd/pull/5830: "Unrestricted unions can have fields that have destructors, postblits, or invariants. It's up to the user to call them correctly, the compiler does not automatically generate calls to them." So this is actually expected behavior in unions, and the spec is wrong.