[Bug c++/92181] initializer_list & string_view result in "modification of '<temporary>' is not a constant expression

[Bug c++/92181] initializer_list & string_view result in "modification of '<temporary>' is not a constant expression

[hyena at hyena dot net.ee]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92181

Erich Erstu <hyena at hyena dot net.ee> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hyena at hyena dot net.ee

--- Comment #3 from Erich Erstu <hyena at hyena dot net.ee> ---
I started getting the same error after upgrading to GCC 9.3.0.

The problem in my case is either related to the use of std::pair in constexpr
or the fact that I have nested instances of std::initializer_list.

The workaround was to replace std::pair with a custom struct as seen here:

struct zone_name_root_variant_type {
    const char *name;
    std::initializer_list<ZONE_NAME_AFFIX> affixes;
};

struct zone_name_root_type {
    ZONE_NAME_ROOT index;
    const char *region;
    std::initializer_list<
        zone_name_root_variant_type
        /*
        std::pair<
            const char*,
            std::initializer_list<ZONE_NAME_AFFIX>
        >
        */
    > variants;
};

static constexpr const zone_name_root_type zone_name_root_table[] = {
    {
        ZONE_NAME_ROOT::UNKNOWN, "Region",
        {
            {  "",     { ZONE_NAME_AFFIX::UNKNOWN } }
        }
    },
    { ZONE_NAME_ROOT::NONE, "", { } }
};

[Bug c++/92181] initializer_list & string_view result in "modification of '<temporary>' is not a constant expression

[hyena at hyena dot net.ee]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92181

--- Comment #4 from Erich Erstu <hyena at hyena dot net.ee> ---
I also found out that when I try to populate a constexpr array using a trivial
constexpr function that passes on the argument initializer list then I get the
same error.

This does not work any more within the definition of a constexpr array:

constexpr room_desc_part_type make(
    ROOM_DESC_PART part, std::initializer_list<const char *> args
) {
    return
#if __cplusplus <= 201703L
    __extension__
#endif // __cplusplus
    room_desc_part_type{
        .index = part,
        .arguments = args
    };
}

[Bug c++/92181] initializer_list & string_view result in "modification of '<temporary>' is not a constant expression

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92181

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ppalka at gcc dot gnu.org
             Status|NEW                         |RESOLVED
   Target Milestone|---                         |12.3
         Depends on|                            |107079
         Resolution|---                         |FIXED

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Looks like this is fixed for GCC 12.3+ by the fix for PR107079.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107079
[Bug 107079] [10/11 Regression] ICE initializing lifetime-extended constexpr
variable that stores its this pointer