Re: Template-based implementation of Sutter's exception-safe operator= idiom

From: Steven E. Harris (seh_at_panix.com)
Date: 08/21/04 

Date: 20 Aug 2004 23:56:00 -0400

David Abrahams <dave@boost-consulting.com> writes:

> Any time you make assignment give the strong guarantee by copying
> and swapping, you force anyone who wants to use assignment in an
> operation which doesn't need that strong guarantee to pay for the
> unneccessary copy, which could be very expensive.

For those who do need the strong guarantee at a higher level, how do
they go about getting it? I understand the "SGI argument" about
concurrency control, but I'm missing the analogous option here to add
exception-safe "locks" at a higher level.

Take your example where a client wants an assignment followed by
push_back() to have the strong guarantee.¹ Is this a potential
solution?

// Neither compiled nor tested.

template <typename C, typename T>
C& safe_assign_push(C& dest, C const& src, T const& val)
{
    C temp( src );
    temp.push_back( val );
    dest.swap( temp );
    return dest;
}

Footnotes:
¹ http://lists.boost.org/MailArchives/boost/msg36928.php 

-- 
Steven E. Harris
      [ See http://www.gotw.ca/resources/clcm.htm for info about ]
      [ comp.lang.c++.moderated.    First time posters: Do this! ]

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