On Wed, 14 Nov 2018, Jakub Jelinek wrote:
> Hi!
>
> As mentioned in the PR, with GCC before 4.3 one can't instantiate std::pair
> where one or both of the template parameters are reference types, because
> the std::pair constructor has arguments references to the template parameter
> types and the CWG that resolved hasn't been applied to those compilers.
>
> The following patch works around it by not returning
> std::pair<const Key &, Value &> object, but instead a different class that
> holds the two references and has conversion operator to std::pair.
>
> If that conversion operator isn't acceptable, in the PR there is another
> patch which adjusts the (so far) two spots which need to be changed in that
> case.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux (using GCC 7 as
> bootstrap compiler) and tested on the preprocessed source with GCC 4.1.
> Ok for trunk?
Works for me if C++ people have no better idea.
Thanks,
Richard.
> 2018-11-13 Jakub Jelinek <ja...@redhat.com>
>
> PR bootstrap/86739
> * hash-map.h (hash_map::iterator::reference_pair): New class.
> (hash_map::iterator::operator*): Return it rather than std::pair.
>
> --- gcc/hash-map.h.jj 2018-07-11 22:22:01.250836509 +0200
> +++ gcc/hash-map.h 2018-11-13 20:45:38.463037081 +0100
> @@ -223,10 +223,23 @@ public:
> return *this;
> }
>
> - std::pair<const Key&, Value&> operator* ()
> + /* Can't use std::pair here, because GCC before 4.3 don't handle
> + std::pair where template parameters are references well.
> + See PR86739. */
> + struct reference_pair {
> + const Key &first;
> + Value &second;
> +
> + reference_pair (const Key &key, Value &value) : first (key), second
> (value) {}
> +
> + template <typename K, typename V>
> + operator std::pair<K, V> () const { return std::pair<K, V> (first,
> second); }
> + };
> +
> + reference_pair operator* ()
> {
> hash_entry &e = *m_iter;
> - return std::pair<const Key&, Value&> (e.m_key, e.m_value);
> + return reference_pair (e.m_key, e.m_value);
> }
>
> bool
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
