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From: "leonid at volnitsky dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/54859] New: constexpr in template aliase rejected as non-constant
Date: Mon, 08 Oct 2012 17:05:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D54859

             Bug #: 54859
           Summary: constexpr in template aliase rejected as non-constant
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: leonid@volnitsky.com


clang-3.2 and gcc-4.7.2 compiles,  gcc-4.8 rejects:

--------------------------------------------------------------------------
// enbale_if=20
template <bool B, class T =3D void>=20=20=20=20
struct enable_if  { typedef T type; };=20

template <class T>=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
struct enable_if<false, T>   {};

// template alias
template<bool Cnd, class T=3Dvoid>=20
using  eIF =3D typename enable_if <Cnd,T>::type;

// f  - this compiles
template<bool B=3Dtrue>=20
typename enable_if<!B, int>::type f() { return 20; }

// ff - error: integral expression =E2=80=98! B=E2=80=99 is not constant=20
template<bool B=3Dtrue>=20
eIF<!B, int>  ff() { return 20; }

int main() {}
---------------------------------------------------------------------------=
=20

This seams to be related to bug 54648,  where I found bad commit to be 1914=
12