On Fri, 1 Oct 2021, 23:30 Martin Sebor via Gcc, <gcc@gcc.gnu.org> wrote:
> On 10/1/21 11:44 AM, Florian Weimer wrote: > > * Martin Sebor via Gcc: > > > >> I'd expect TYPE_NEEDS_CONSTRUCTING to be non-zero in the middle end > >> for any C++ type with a user-defined ctor, but in some of my testing > >> I see it's actually zero for std::string, at least in some instances > >> (but nonzero for other types with ctors). Is there something special > >> about std::string that makes it so? (If this is intentional, how can > >> I create my own type that has a user-defined ctor and also a zero > >> TYPE_NEEDS_CONSTRUCTING?) > > > > I assume by writing an explicit default constructor: > > > > T() = default; > > Yes, but in a class that also defines (non-defaulted) ctors > TYPE_NEEDS_CONSTRUCTING() is nonzero. > > I'm looking for a type that defines a ctor (the above just declares > one) that has a zero for TYPE_NEEDS_CONSTRUCTING(T). GCC documents > the macro as: > > /* Indicates that objects of this type must be initialized by calling a > function when they are created. */ > > So assuming TYPE_NEEDS_CONSTRUCTING(std::string) is supposed to return > zero (i.e., it's not a bug or some oddity I'm seeing) I want to know > how to define a class like it, with one or more user-defined ctors, > for which TYPE_NEEDS_CONSTRUCTING() also returns zero. Otherwise, > if it's a bug, I'll see if I can come up with a test case for it. > This seems surprising, I don't know why std string would need or get any special treatment in this respect. I'm not aware of any magic for std:: string except for the custom mangling that is defined by the ABI for it (which doesn't apply to our new std::__cxx11::string anyway). >
