Trivial copy assignment operator overwrites members not being copied (original) (raw)

Extended Description

In the following, the operator= used by Q's defaulted copy assignment operator for the d subobject is a copy assignment operator of B: that is, it does not copy the b0 member of d.
The expected behaviour is observed when Q's copy assignment operator is explicitly defaulted after its first declaration, but not if it is explicitly defaulted on its first declaration.

SOURCE ():

extern "C" void abort(void); struct B0 { int b0; };

struct B { B &operator=(const B &) = default; int x; };

struct D : B0, B { using B::operator=; private: D &operator=(const D &) && = default; };

struct Q { Q &operator=(const Q &) = default; D d; }; //Q &Q::operator=(const Q &) = default;

Q qa, qb; int main(void) { qb.d.b0 = 42; qb = qa; if (qb.d.b0 != 42) abort(); }

COMPILER INVOCATION:

clang++ -xc++ -std=c++2a -o inhtrivcpyassn -

INVOCATION AND OUTPUT OF RESULTING EXECUTABLE:

> ./inhtrivcpyassn; printf '(rc=%d)\n' "$?"
Aborted                 ./inhtrivcpyassn
(rc=134)

EXPECTED RUN OUTPUT:

COMPILER VERSION INFO (clang++ -v):

clang version 7.0.0 (https://github.com/llvm-mirror/clang.git f38834898ad991aec557e2a609c6b7c3b288bf10) (https://github.com/llvm-mirror/llvm.git 433eb70569ee6379cdd5181e72b9193fdb0a39dd)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/wandbox/clang-head/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.4.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/6.0.0
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.4.0
Candidate multilib: .;@m64
Selected multilib: .;@m64