Re: gcc7 build error with recent tip

[Daniel J Sebald]

On 06/24/2017 11:21 AM, Dmitri A. Sergatskov wrote:
> On Sat, Jun 24, 2017 at 10:59 AM, John W. Eaton <address@hidden
> <mailto:address@hidden>> wrote:
>
>
>     I admit this code is a bit tricky.  I was trying to come up with a
>     way to use a single template that would cover both of these cases:
>
>       static octave_value
>       dump_container_map (const std::map<std::string,
>     std::list<std::string>>&)
>
>       static octave_value
>       dump_container_map (const std::map<std::string,
>     std::map<std::string>>&)
>
>     It works for me with gcc version 6.3.0 20170516 (Debian 6.3.0-18).
>
>
> ​It is quite possible this is a bug in gcc7.1.1.
> I filled a bug:
>
> ​https://bugzilla.redhat.com/show_bug.cgi?id=1464612
>
> would like to see what Jakub has to say about it.

Yes, that is quite possible, based upon the error message.  The compiler 
identifies the proper candidate, but it is telling us that the candidate 
expects only one argument.  I.e.,

../src/libinterp/corefcn/symtab.cc:1424:1: note: candidate: 
template<class V, template<class ...> class C> octave_value 
dump_container_map(const std::map<std::__cxx11::basic_string<char>, C<V> >&)
 dump_container_map (const std::map<std::string, C<V>>& container_map)
 ^~~~~~~~~~~~~~~~~~
../src/libinterp/corefcn/symtab.cc:1424:1: note:   template argument 
deduction/substitution failed:
../src/libinterp/corefcn/symtab.cc:1446:73: note:   candidate expects 1 
argument, 3 provided
        {"precedence_table", dump_container_map 
(m_class_precedence_table)},

but I don't understand where the compiler is getting those number 3 
from.  Here's the definition of m_class_precedence_table:

std::map<std::string, std::set<std::string>> m_class_precedence_table;

That would be either 1 (m_class_precedence_table consider one argument) 
or 2 (expanded m_class_precedence_table).  I think the compiler in this 
case is truncating the template when it sees the word "template" again. 
That would be "1" and perhaps something strange in the compiler expands 
the second "template" into 2 arguments, hence creating 1 + 2 = 3 arguments.

Dan