Bug 18855 – Behavior of Anonymous Union is Undocumented

In the DLang specification here: https://dlang.org/spec/struct.html#AnonUnionDeclaration It is said that anonymous unions can be declared, but the ramifications of this are never clarified. Those coming from C++ will suspect that it makes the anonymous union members members of the containing object, but for those coming from Java or another language, this behaviour will seem unexplained. Example below: ``` void main() { import std.stdio; struct Bob { int a; union { // Anonymous union. int b; int c; } union Cat { int d; int e; } Cat cat; } Bob bob = Bob(1, 2); assert(bob.a == 1); assert(bob.b == 2); assert(bob.c == 2); bob.cat = Bob.Cat(3); // assert(bob.d == 3); // ERROR, Bob has no property 'd'. assert(bob.cat.d == 3); // OK } ```

@ntrel updated dlang/dlang.org pull request #3355 "[spec/struct] Add 'Union Literals' & 'Anonymous Structs & Unions'" fixing this issue: - Fix issues 18855 and 21188 - Add 'Union Literals' & 'Anonymous Structs & Unions' Fix Issue 21188 - Anonymous structs - not described. Fix Issue 18855 - Behavior of Anonymous Union is Undocumented. Fix: Non-overlapping union field data is not default initialized, it is zeroed. https://github.com/dlang/dlang.org/pull/3355