https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96268
Bug ID: 96268
Summary: class-type NTTP CTAD for string-literal aggregate
fails on aggregate initialization
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: wjwray at gmail dot com
Target Milestone: ---
I understand that gcc is ahead of the standard in its implementation of class-
type NTTP, along with CTAD and accepting braced init-lists as template Args.
Thanks for implementing it. This bug is an edge case in the handling of a
braced string literal argument for a 'static string' - a motivating use case.
Example code on Compiler Explorer https://godbolt.org/z/sMWhbx
Given this 'static_string' implementation, as an aggregate (no constructors):
template <int N>
struct static_string { char chars[N]; /* operator<=> */ };
template <int N>
static_string(char const(&)[N]) -> static_string<N>;
A variable can be deduced and initialized from braced string-literal:
static_string hi = {"hi"}; // Accepted
(Aggregate-init of char array from string-literal being a special case.)
However, this same braced string-literal fails as a class-type NTTP:
template <static_string str> struct name {};
using Hi = name<{"hi"}>; // Reject, should accept?
It appears to CTAD-deduce correctly then fail on the aggregate initialization:
error: could not convert '{"hi"}' from '<brace-enclosed init list>
to 'static_string<3>'
| name<{"hi"}>;
| ^
| |
| <brace-enclosed initializer list>
