I've got a variant
class. It has a pair of constructors:
/// Construct and fill.
template <typename T>
inline
variant (const T& t)
{
YYASSERT (sizeof (T) <= S);
new (buffer.raw) T(t);
}
template <typename T>
inline
variant (T&& t)
{
YYASSERT (sizeof (T) <= S);
new (buffer.raw) T(std::move(t));
}
Now I've called those constructors in this code:
parser::sy开发者_C百科mbol_type
parser::make_IDENTIFIER (const Wide::ParsedFile::Identifier*& v)
{
return symbol_type (token::IDENTIFIER, v);
}
symbol_type
takes a variant
as it's second argument in this specific constructor, and v
is being implicitly converted.
However, MSVC will try to use the rvalue reference constructor instead of using the other constructor, resulting in a compilation error when it attempts to new
a reference. Why is that, and how can I make it stop?
You generally should not overload a templated T&&
function. You should instead have the single function which forwards:
template <typename T>
inline
variant (T&& t)
{
typedef typename std::remove_reference<T>::type Tr;
YYASSERT (sizeof (Tr) <= S);
new (buffer.raw) Tr(std::forward<T>(t));
}
This has the functionality of your two overloads, while avoiding the problem of picking the wrong one.
I believe (not positive) that these are the two variants in your overload set:
varaint<const Wide::ParsedFile::Identifier*>(const Wide::ParsedFile::Identifier*const&)
varaint<const Wide::ParsedFile::Identifier*&>(const Wide::ParsedFile::Identifier*&)
And the second one wins because it is more specialized than the first (I'm making an educated guess, I'm not 100% positive).
The second template would be a better match, because the const
specifiers are in different places in your function and in the first constructor.
In the first overload you will have T being deduced as
const Wide::ParsedFile::Identifier*
And then creating a const reference to that type. That adds an extra const.
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