Re: [boost] [variant] awkward recursion

Subject: Re: [boost] [variant] awkward recursion
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2012-11-02 10:21:59

On 31/10/12 19:02, Dave Abrahams wrote:

> namespace wrapper
> {
>    struct value;
>
>    template <class T, class U>
>    struct mymap : std::map<T,U>
>    {
>        enum { _size = sizeof(T)+sizeof(U) }; // error if T or U are incomplete
>    };
>    typedef mymap<std::string, value> object;

This line instantiates the declaration of std::map<std::string, value>, 
but not its definition, which is why you don't get any error (doing 
those sizeofs inside the declaration itself will yield errors though of 
course).

I'm no expert at standardese but it seems class template instantiation 
usually refers to instantiating the definition, which would mean that 
this is indeed allowed.