https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94983
Bug ID: 94983 Summary: Empty list initialization of aggregate class with deleted default ctor rejected in C++14 and C++17 Product: gcc Version: 9.3.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c++ Assignee: unassigned at gcc dot gnu.org Reporter: andrey.vihrov at gmail dot com Target Milestone: --- Consider the following C++ sample: struct S { S() = delete; }; void foo() { new S{}; } In C++11 to C++17, S is an aggregate type. In C++20, S is not an aggregate type (has a user-declared constructor). In C++11, list initialization will perform value initialization if the initializer list is empty and the class has a default constructor; otherwise, if the class is an aggregate type, aggregate initialization will be performed. Since C++14, the order is reversed: if the class is an aggregate type, aggregate initialization will be performed; otherwise, value initialization will be performed if the initializer list is empty and the class has a default constructor. Value initialization performs default initialization for S. Default initialization calls the deleted default constructor. Aggregate initialization has no effect and succeeds for S. Putting this together: * In C++11: S should be default-initialized and fail to compile * In C++14: S should be aggregate-initialized and succeed * In C++17: S should be aggregate-initialized and succeed * In C++20: S should be default-initialized and fail to compile GCC correctly rejects the sample with -std=c++11 and -std=c++2a. However, the sample is also incorrectly rejected with -std=c++14 and -std=c++17. Additionally, a variation of the sample gives different results, although it should behave the same: void foo() { S{}; } GCC gives: * -std=c++11: OK (incorrect) * -std=c++14: OK (correct) * -std=c++17: OK (correct) * -std=c++2a: rejected (correct) It is understandable, though, if GCC does not intend to change behavior for C++11. gcc -v: Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/9.3.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: /build/gcc/src/gcc/configure --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-pkgversion='Arch Linux 9.3.0-1' --with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++,d --enable-shared --enable-threads=posix --with-system-zlib --with-isl --enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object --enable-linker-build-id --enable-lto --enable-plugin --enable-install-libiberty --with-linker-hash-style=gnu --enable-gnu-indirect-function --enable-multilib --disable-werror --enable-checking=release --enable-default-pie --enable-default-ssp --enable-cet=auto gdc_include_dir=/usr/include/dlang/gdc Thread model: posix gcc version 9.3.0 (Arch Linux 9.3.0-1)