[LLVMbugs] [Bug 11764] New: decltype(MyClass()) doesn't work as a trailing return type

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=11764

             Bug #: 11764
           Summary: decltype(MyClass()) doesn't work as a trailing return
                    type
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++0x
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: jyasskin at google.com
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified


Given the following program:

#include <typeinfo>
#include <iostream>
#include <vector>

template<typename T>
struct array_ref {
    array_ref(const std::vector<T>& v) {}
};

template<typename T>
auto make_array_ref(const T& t) -> decltype(array_ref<int>(t)) {
    return array_ref<int>(t);
}

template<typename T>
void WriteType(T t) {
    std::cout << typeid(decltype(array_ref<int>(t))).name() << '\n';
}

int main() {
    std::vector<int> v;
    WriteType(v);
    make_array_ref(v);
}

-----------
clang++ -std=c++11 gives the following error:

test.cc:12:12: error: no viable conversion from 'array_ref<int>' to
'decltype(array_ref<int>(t))'
    return array_ref<int>(t);
           ^~~~~~~~~~~~~~~~~
1 error generated.

The lack of 'aka' is bug 10405, but I believe the code should compile as-is. It
does with gcc-4.6, and the decltype() expression is exactly the same as the
returned expression. Further, when I comment out make_array_ref(), clang and
gcc print "9array_refIiE" (array_ref<int>), which is the type of the return
value.

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