aaron.ballman added inline comments.
================
Comment at: clang/lib/Parse/ParseDecl.cpp:5592
+bool Parser::isConstructorDeclarator(bool IsUnqualified, bool DeductionGuide,
+ bool IsFriend) {
TentativeParsingAction TPA(*this);
----------------
erichkeane wrote:
> aaron.ballman wrote:
> > shafik wrote:
> > > Instead of adding yet another `bool` flag maybe we can consider using
> > > something like `enum isFriend : bool {No, Yes}`.
> > >
> > > I am sure @aaron.ballman will want to chime in here as well.
> > Heh, so this is where I get worried about the scalability of using enums
> > for these. We really want to use three different enums here, but do we
> > really want to *add* three different enums? I'm unconvinced.
> >
> > However, if we can come up with some template magic to allow for named bool
> > parameters as a generic interface, that would be valuable to use.
> I prefer enums over bools TBH, even if we end up with a million of then
> somewhere.
>
> That said, what about:
>
> https://godbolt.org/z/Kz6jdjobj
>
> ```
> template<typename SpecificThing>
> class Is {
> Is(bool v) : value(v){}
> public:
> bool value;
> static const Is Yes() { return Is{true};}
> static const Is No() { return Is{false};}
>
> operator bool() { return value; }
> };
>
> class Friend{}; // #1
>
> void foo(Is<Friend> f) {
> if (f) {
> ///...
> }
> }
>
> void baz() {
> foo(Is<Friend>::Yes());
> }
> ```
>
> Adding a 'new' thing is as simple as just adding #1 for anything we care
> about. We might want to put them in a namespace of some sort, but perhaps
> not awful?
Yeah, this is along the lines of what I was thinking of! However, I'm still
concerned about that approach because it involves adding a new type for every
situation we have a bool. Empty classes to use as a tag definitely works, but I
was hoping we could use a string literal rather than a tag type so that we
don't have the extra compile time overhead of adding hundreds of new empty
classes. e.g.,
```
void foo(Is<"Friend"> f) {
if (f) {
// ...
}
}
void baz() {
foo(Is<"Friend">::Yes); // Yay
foo(Is<"Enemy">::Yes); // Error for type mismatch with Is<"Friend">
}
```
However, that might require compiling with C++20 (I don't recall), so it may
not be a viable idea.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D53847/new/
https://reviews.llvm.org/D53847
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