VS2015 internal compiler error when calling base class constexpr method

Question

the following code produces an internal compiler error (VS2015)

struct A
{
    constexpr A(){}
    constexpr int bar()
    {
        return 3;
    }
};

struct B : A
{
    constexpr B(){}
    constexpr int foo()
    {
        return A::bar();
    }
};

int main()
{
    constexpr B b;
    constexpr int dummy = b.foo();
    return 1;
}

However, if i'd remove the A:: qualifier:

constexpr int foo()
{
    return bar();
}

it will be compiled. problem arises when these methods have the same name, and I need to invoke the base class method. (e.g. when using recursive template inheritence)

any workarounds?

How about this->A::bar();?

Daniel Frey
– Daniel Frey

2015-05-09 12:55:50 +00:00
Commented May 9, 2015 at 12:55 — Daniel Frey
– Daniel Frey, Commented May 9, 2015 at 12:55
@DanielFrey same same

yoyo
– yoyo

2015-05-09 13:19:52 +00:00
Commented May 9, 2015 at 13:19 — yoyo
– yoyo, Commented May 9, 2015 at 13:19
Have you filed a bug?

T.C.
– T.C.

2015-05-09 16:36:51 +00:00
Commented May 9, 2015 at 16:36 — T.C.
– T.C., Commented May 9, 2015 at 16:36

dened · Accepted Answer · 2015-05-16 19:40:48Z

The actual problem is b is declared as const (constexpr implies const on objects) and you are trying to call non-const (since C++14, constexpr doesn't imply const on methods, see here) method with the const object...

According to the standard, you should not be able to solve the problem by simply removing A:: nor by the static_cast the way you did. Pre-RTM version of Visual Studio 2015 allows you to do this only because its support for constexpr is preliminary and very buggy. C++11 constexpr (but unfortunately not C++14 extended constexpr) expected to be fully supported in the RTM version of VS 2015 (see here).

The correct version of your code is:

struct A
{
    constexpr A(){}
    constexpr int bar() const
    {
        return 3;
    }
};

struct B : A
{
    constexpr B(){}
    constexpr int foo() const
    {
        return A::bar();
    }
};

int main()
{
    constexpr B b;
    constexpr int dummy = b.foo();
    return 1;
}

yoyo · Accepted Answer · 2015-05-09 13:26:12Z

1

Found a solution. "this" should be casted to const A*:

struct B : A
{
    constexpr B(){}
    constexpr int foo()
    {
        return static_cast<const A*>(this)->bar();
    }
};

Also works when the methods have the same name.

answered May 9, 2015 at 13:26

yoyo

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