Re: [Boost-users] [type_traits]: is_boost_optional?

Subject: Re: [Boost-users] [type_traits]: is_boost_optional?
From: Stefan Strasser (strasser_at_[hidden])
Date: 2010-09-01 09:30:10

Zitat von Roland Bock <rbock_at_[hidden]>:

> Hi,
>
> is there something in Boost.TypeTraits (or somewhere else) that  
> allows me to check if a type is a boost::optional?
>
> I'd like to do something like this:
>
> template<typename T>
> typename enable_if<is_boost_optional<T> >, T::value_type>::type  
> foo(const T&);

there is nothing in type traits, but you can easily check for a  
specific (template) type:

template<typename T>
struct is_optional : mpl::false_{};

template<typename T>
struct is_optional<optional<T> > : mpl::true_{};

I don't see why you can't use an overload for boost::optional in the  
first place though:

typename optional<T>::value_type foo(optional<T> const &);