Re: [boost] unique_ptr for C++03

Subject: Re: [boost] unique_ptr for C++03
From: Andrew Ho (helloworld922_at_[hidden])
Date: 2013-08-05 02:12:32

> Oops, I removed the delegated constructor calls and used a call to a 
> function which may not exist if the type is not convertible. However, the 
> compiler error message this generates is less intuitive than usually 
(which 
> is saying something for template compiler messages :P).
> 

update: I switched to a default function parameter to an internal nat 
struct, this should make the compiler message easier to understand without 
forcing/allowing users to do something "non-standard".

In my tests, I have come up to a problem:

std::unique_ptr allows the user to "move-construct" from a std::auto_ptr. 
However, this class is not marked as to be movable with move emulation.

There are two solutions I could think of:

1. Remove the constructor if there's no true rvalue refs.
2. "Move-construct" from a std::auto_ptr&.

1 disallows some behavior which is standard, and 2 allows more behavior than 
the standard allows. Which should we go with, or does anyone know of a 
better work-around?

My personal vote is for 1 as the user could just as easily do:

// still valid standard c++11
my_uptr(my_aptr.release());

With 2 there is no way to stop the user from doing something non-standard 
compliant:

// standard c++11 requires std::move(my_aptr)
my_uptr(my_aptr);

I think this issue and support for std::nullptr_t are the only two remaining 
pieces which would allow this class to be used in a non-standard compliant 
manner.