Re: [Boost-users] [value_initialized] when T is const

Subject: Re: [Boost-users] [value_initialized] when T is const
From: Niels Dekker - address until 2010-10-10 (niels_address_until_2010-10-10_at_[hidden])
Date: 2009-09-19 17:56:51

Edward Diener wrote:
> I like the idea of using value_initialized for a variable to initialize 
> a value to its value intialized value when no initial value is given. 
> But if an initial value is subsequently given it does not work if the T 
> is a const type. Was this intended ?

I think so, yes.  (Nit picking: a subsequently given value is not an 
initial value!)

> It can be argued that if one is specifying a const type and one wants to 
> initialize the object of that type to a non-value initialized value, 
> simply do not use boost::value_initialized.

Yes, I think so too.  (I'm sorry!)

> It would seem that this limitation could be lifted if the 
> boost::value_initialized template had a constructor which enabled one to 
> initialize the value in cases where initialization to a value 
> initialized state was not desired. Then, despite T being a const type, 
> one could initialize the variable to a specific value in the 
> constructor, while keeping the current semantics which disallow changing 
> the value of a const type once it has been initialized.

Of course, technically speaking, a constructor could be added to 
value_initialized<T> that accepts a T argument, and copies its value. 
But if so, value_initialized<T> would no longer guarantee to always 
deliver value-initialized objects. Wouldn't that be a drawback?

BTW There's still a fix of a "const issue" of value_initialized 
underway. Please have a look:  https://svn.boost.org/trac/boost/ticket/2548

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