Re: [boost] Improving the assignment operators of various Boosttypes

Subject: Re: [boost] Improving the assignment operators of various Boosttypes
From: David Abrahams (dave_at_[hidden])
Date: 2008-09-11 14:19:15

on Thu Sep 11 2008, Gevorg Voskanyan <v_gevorg-AT-yahoo.com> wrote:

>> David Abrahams wrote:
>>
>>> on Thu Sep 11 2008, Gevorg Voskanyan wrote:
>>  
>> [snip]
>>
>>> > AFAIU, a swapping assignment operator taking the parameter by const ref adheres
>>> > to the strong exception safety guarantee, whereas the one taking the parameter
>>> > by value fulfills the nothrow guarantee. Not sure how practical and/or relevant
>>> > the difference in this context is, though.
>>> >
>>> > Is my observation above correct?
>>> 
>>> Well, technically, yeah... although the expression that does the
>>> assignment can still throw, so I don't think it makes much difference to
>>> say that it's nothrow.  In other words, if I give you
>>> 
>>>     f(std::string);  // nothrow
>>>     g(std::string&); // strong guarantee
>>> 
>>> For all practical purposes, you know that f and g have equivalent
>>> exception behavior because std::string's copy ctor can throw.
>>
>> True, that's why I questioned the practicality of this difference :)
>> Except perhaps for documenting a function's exception safety. Should it be
>> considered while making aforementioned assignment operators in boost to take the
>> argument by value?

If you're asking whether such functions should be documented as nothrow
after the modification, I think they should: it could be useful
information for move-only types (with nonthrowing move ctors).

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com