Bug 19150 – Union member assignment causes invalid destructor call in @safe code

The following code compiles without errors and produces an erroneous call to HasDtor's destructor: --- struct HasDtor { int n; ~this() @safe { import std.stdio: writeln; writeln("Called destructor with n = ", n); } } union U { float n; HasDtor h; } @safe void main() { U u = { n : 1 }; u.h = HasDtor(2); } --- Output: Called destructor with n = 1065353216 Because there is no way to know at compile time whether the union member being assigned to is valid, assignment to a member of a union that includes any members with destructors should be forbidden in @safe code. In addition, since the language must rely on the programmer to manually destroy the appropriate union member in @system code, the automatic destructor call is at best redundant and at worst undefined behavior. Therefore, it should be omitted.

*** This issue has been marked as a duplicate of issue 19122 ***