static function in template class: gcc vs VS

Question

The following c++ code compiles and works with Visual Studio 2017, but gives error "expected primary-expression before '>' token" with gcc 5.0. Any idea why? Description is a struct, and Description::add is a function template.

template <class X>
struct DataPoint
{
    X value;

    DataPoint()
    : value(0.) {}

    DataPoint( X value )
    : value(value) {}

    static void describe(Description< DataPoint<X> > & desc)
    {
        desc.add<X>("f", ".", offsetof(DataPoint<X>, value));
    }
}

In fact VS doesn't even complain when the DataPoint template type is not specified:

static void describe(Description<DataPoint> & desc)
{
    desc.add<X>("f", ".", offsetof(DataPoint, value));
}

`DataPoint` (without supplying template arguments) is the *injected-class-name* — Ben Voigt, Feb 26 '18 at 07:03
different lexical parsers interpret non-standard things differently. — Justin Randall, Feb 26 '18 at 07:03

score 2 · Accepted Answer · answered Feb 26 '18 at 07:05

2

Your code is not standard C++. The add in desc.add<X> is a dependent name, so the compiler doesn't know if it is a template. Visual C++ still doesn't implement the entire two-phase lookup, so it's not surprising that it lets this through. But g++ (and clang, etc) require you to use the template keyword.

desc.template add<X>("f", ".", offsetof(DataPoint, value));

answered Feb 26 '18 at 07:05

Ben Voigt

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Thanks! My code now compiles on both windows and POSIX. – psilouette Feb 26 '18 at 23:21

static function in template class: gcc vs VS

1 Answers1