Re: [boost] [utility/value_init] boost::value_initialized<T> direct-initialized?

Subject: Re: [boost] [utility/value_init] boost::value_initialized<T> direct-initialized?
From: Niels Dekker - address until 2010-10-10 (niels_address_until_2010-10-10_at_[hidden])
Date: 2010-04-01 03:31:32

Jeffrey Hellrung wrote:
>> The templated constructor should be explicit, because otherwise
>> things like
>>
>> boost::initialized<std::vector<int> > v = 10;
>>
>> would compile. IMHO, it's okay if implicit
>> conversions that would normally work for
>> the contained type don't work, since this errs
>> on the side of safety, but it isn't okay to make
>> all conversions implicit.
>
> Agreed.

Leaving out the "explicit" keyword from the initialized(const T&) 
constructor of initialized<T> won't make Steven's example compile (as I 
wrote before).

In what particular situation would you need to use 
boost::initialized<T>, including the new initialized(const T&) 
constructor, instead of just the old value_initialized<T>?

I think /the/ motivating use case for boost::initialized<T> is about 
member data initialization:

   template <typename T> class foo
   {
     std::string m_name;
     boost::initialized<T> m_data;
   public:
     foo();
     foo(const foo&);
     foo(const T&, std::string);
   };

In this case, some of foo's constructors may want m_data to be 
value-initialized, but others need to do direct-initialization.

Do you agree that its support for member data initialization would be 
the main reason for having boost::initialized<T>?

> And I don't think the boost::direct_initialized tag is
> necessary,
> MSVC compiler bugs be damned.

Sorry, I'm not sure what you mean. It's certainly important to me to 
have something that works on MSVC.

Kind regards,

   Niels
-- 
Niels Dekker
http://www.xs4all.nl/~nd/dekkerware
Scientific programmer at LKEB, Leiden University Medical Center