On Thu, Oct 11, 2018 at 8:25 PM Marek Polacek <pola...@redhat.com> wrote:
>
> On Thu, Oct 11, 2018 at 11:35:23AM -0400, Jason Merrill wrote:
> > > + /* [dcl.fct.spec]
> > > + "the constant-expression, if supplied, shall be a contextually
> > > + converted constant expression of type bool." */
> > > + expr = build_explicit_specifier (expr, tf_warning_or_error);
> > > + /* We could evaluate it -- mark the decl as appropriate. */
> > > + if (expr == boolean_true_node)
> > > + set_and_check_decl_spec_loc (decl_specs, ds_explicit, token);
> > > + else if (explicit_specifier)
> > > + /* The expression was value-dependent. Remember it so that we
> > > can
> > > + substitute it later. */
> > > + *explicit_specifier = expr;
> >
> > What if expr == boolean_false_node?
>
> Then we proceed like no explicit was present and the decl isn't marked as
> explicit/nonconverting. Perhaps I could have made this clearer with
>
> else if (expr == boolean_true_node)
> /* Don't mark the decl as explicit. */;
>
> or somesuch.
Yes, and also so that we don't store the false as a "dependent" specifier.
> > > + /* Handle explicit(dependent-expr). */
> > > + if (DECL_HAS_DEPENDENT_EXPLICIT_SPEC_P (t))
> > > + {
> > > + tree spec = lookup_explicit_specifier (t);
> > > + spec = tsubst_copy_and_build (spec, args, complain, in_decl,
> > > + /*function_p=*/false,
> > > + /*i_c_e_p=*/true);
> > > + spec = build_explicit_specifier (spec, complain);
> > > + DECL_NONCONVERTING_P (t) = (spec == boolean_true_node);
> > > + }
> >
> > What if spec is still dependent, e.g. after partial substitution of a
> > member template?
>
> Something like this?
>
> template<typename> struct A {
> template<typename T, int N = 0>
> explicit(N) operator T();
> };
>
> void
> bar ()
> {
> A<int> a;
> int i = a;
> }
>
> This also seemed to work: if spec is still dependent, the decl isn't marked as
> DECL_NONCONVERTING_P, and we'll try again after deduction (fn_type_unification
> in add_template_candidate).
Does it also work if N is true? What if the specifier depends on
template parameters from both the enclosing class and the member
template?
Jason
