Re: Add and use a Transform data type (issue 344970043 by address@hidden)

[David Kastrup]

Hans Åberg <address@hidden> writes:

>> On 22 Jun 2018, at 11:09, David Kastrup <address@hidden> wrote:
>> 
>> Hans Åberg <address@hidden> writes:
>> 
>>>> You could also do it as a constructor, if you prefer its syntax and
>>>> don't mind implementing yet another one:
>>>> 
>>>>   explicit Transform(const Transform *t) ...
>>> 
>>> One can also use a tag type argument in the constructor:
>>>  struct make_t {};
>>>  constexpr make_t make{};
>> 
>> What would that be good for?
>
> There are various uses in the C++ library. I found it useful for in a 
> reference class I wrote:
>   template<class A>
>   class ref {
>   protected:
>     A* data_ = nullptr;
>
>   public:
>   ...
>     template<class... B>
>     ref(make_t, B&&... bs) : data_(finalize(new (collect) A(bs...))) {}
>   };
> A direct constructor taking an operator new pointer would not be able to do 
> the GC registering. 
>
> It admits a syntax:
>   ref<A> a(make, ...);
>   auto a = ref<A>(make, ...);
> with the ... arguments passed to the A constructor.

What would that be good for concerning this issue?

-- 
David Kastrup