[cfe-dev] (no subject)

[Csaba Raduly]

Compiling the following code:
#include <memory>
#include <vector>
#include <initializer_list>

struct C {
    std::vector< std::unique_ptr<int> > vec;

    C(std::initializer_list< std::unique_ptr<int> > init)
    : vec(std::make_move_iterator(init.begin()),
          std::make_move_iterator(init.end()))
    {}
};

with clang version 3.6.0 (trunk 222993) (llvm/trunk 222992)
resulted in a perplexing message:

In file included from wtf.cc:1:
In file included from
/usr/local/bin/../lib/gcc/x86_64-unknown-linux-gnu/4.9.0/../../../gcc/x86_64-unknown-linux-gnu/4.9.0/include/c++/memory:62:
In file included from
/usr/local/bin/../lib/gcc/x86_64-unknown-linux-gnu/4.9.0/../../../gcc/x86_64-unknown-linux-gnu/4.9.0/include/c++/bits/stl_algobase.h:67:
/usr/local/bin/../lib/gcc/x86_64-unknown-linux-gnu/4.9.0/../../../gcc/x86_64-unknown-linux-gnu/4.9.0/include/c++/bits/stl_iterator.h:995:16:
error: binding of reference to type 'unique_ptr<[2 * ...]>' to a value

               
of type 'unique_ptr<[2 * ...]>' drops qualifiers
      { return std::move(*_M_current); }
               ^~~~~~~~~~~~~~~~~~~~~~

I can see no qualifiers to be dropped
(although std::initializer_list gives only const access to its contents)



GCC's error message sheds a bit more light on what's wrong:

/usr/include/c++/4.8/bits/stl_iterator.h:963:37: error: invalid
initialization of reference of type 'std::move_iterator<const
std::unique_ptr<int>*>::reference {aka std::unique_ptr<int>&&}' from
expression of type 'std::remove_reference<const
std::unique_ptr<int>&>::type {aka const std::unique_ptr<int>}'
       { return std::move(*_M_current); }
                                     ^

Note the presence of 'const' in the GCC error message, as opposed to clang
(which makes no mention of const).

Csaba
(please excuse ghastly formatting by Gmail)

-- 
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Life is complex, with real and imaginary parts.
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Torvalds
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