Re: [Boost-users] [Iterator] shared_container_iterator usability

Subject: Re: [Boost-users] [Iterator] shared_container_iterator usability
From: Frank Birbacher (bloodymir.crap_at_[hidden])
Date: 2012-03-19 18:10:18

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hi!

Am 19.03.12 17:28, schrieb Szymon Gatner:
> This way you get 2 heap allocations + shared_ptr<> construction as 
> opposed to just internal allocation of vector (using allocator).
> This is especially bad if returned vector turns out to be empty. In
> that case vector might not do allocation at all so vector creation
> and return are practically free.

The shared_ptr construction means what? The vector will allocate and
the boost::make_shared allocates memory on the heap. The copying of
the shared_ptr is rather cheap in comparison.

One use case: distribute any number of subranges of a shared range.
Imagine a function that returns (by value) a list (or vector) of
substrings (shared_iterator pairs = ranges) of some larger string. The
substrings can shared ownership on the underlying large string. Of
course there are alternatives to shared iterators, but its a valid use
case anyway, I think.

Frank
-----BEGIN PGP SIGNATURE-----
Version: GnuPG/MacGPG2 v2.0.17 (Darwin)
Comment: GPGTools - http://gpgtools.org
Comment: keyserver x-hkp://pool.sks-keyservers.net

iEYEARECAAYFAk9nrsoACgkQhAOUmAZhnmp1igCeP7UeAho8Hc1Q8iQy4x/LOXu9
FYEAnRtyEGOqhEfnRrXWkFG4D3HOsmyY
=bodr
-----END PGP SIGNATURE-----