[boost] Re: move semantics

From: David Abrahams (dave_at_[hidden])
Date: 2004-04-19 11:26:29

Andrea Torsello <torsello_at_[hidden]> writes:

> David Abrahams wrote:
>  
>> 
>> My library is not relying on it being enough.  It's just turning off
>> the mechanisms needed for non-RVO'ing compilers where appropriate.
>
> This is clearly the best thing, which leaves us where we do not provide any
> X(X const &) constructor (explicit or implicit) unless the compiler
> requires it.

Uh, no: when turning off the mechanisms needed for non-RVO'ing
compilers we supply a non-explicit X(X const&) ctor, and no X(X&)
ctor.

>>>>> You still need to convert to temporary in initializer lists, since
>>>>> you cannot use the assigment constructor there, but most likely you
>>>>> would have to do it anyway.
> [...]
>> 
>> That's what the explicit "move(x)" function is for:
>
> exactly, my point was that in initialization lists you probably need to
> convert to temporary with the move(x) function. By "convert to temporary" I
> meant the X::temporary type I had in my examples.  The move_from<X> type in
> your code.

Right... but that "conversion to temporary" is not the same as
*actually* converting to a C++ temporary, which involves making a
copy.

>> Considering that most/all of my ctors' logic is in the initializer
>> list and that the two ctors' initializers will be different, I like
>> having a way to make them the same.
>> 
> [...]
>>> Yes users would still have to provide the initializer lists.
>> 
>> Only one initializer list need be provided, using implicit_cast<> if
>> neccessary.
>
> With complicated initializer lists, I agree that one doesn't want to
> duplicate the list. I guess that this is a personal coding-style issue.

Yes.  And you can take either approach with both technique 1 and
technique 2.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com