C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  iterators::reference - what requirements on it are exposed?          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Alexander Stippler Guest Posted: Sun Dec 28, 2003 2:56 pm    Post subject: iterators::reference - what requirements on it are exposed? Hi, I've got a question concerning iterators. I'm writing some container class and iterators upon it. I have to have typedef typex pointer; typedef typey reference; to be standard conforming. But what semantic requirements does the standard expose on type typey (and typex). If I define reference operator*(), does the object I return have to be (non-const) referencable or can I return a temporary object of typey? If I'm not allowed to, how can I write some iterator and especially operator*(), if I have to create its result on the fly? I hope, I made my question understandable. regards, alex Back to top Nick Hounsome Guest Posted: Sun Dec 28, 2003 3:54 pm    Post subject: Re: iterators::reference - what requirements on it are expos "Alexander Stippler" <stip (AT) mathematik (DOT) uni-ulm.de> wrote Quote: Hi, I've got a question concerning iterators. I'm writing some container class and iterators upon it. I have to have typedef typex pointer; typedef typey reference; to be standard conforming. But what semantic requirements does the standard expose on type typey (and typex). If I define reference operator*(), I forget all the details as to why but apparently to be a standard container it turns out that pointer and reference have to be the obvious types (T*, T&) (perhaps const or volatile but not proxy classes). However you don't have to create standard containers and even the standard contains "non-standard" containers in particular vector<bool> precisely because reference isn't bool& and therefore you cannot take the address of one to get bool*. I think I MAY have come across all this in "Effective C++" or "More Effective C++" The main reason to give the typedef is so that standard algorithms can work with your iterators. If an algorith is supplied an iterator it cannot know directly what the fundamental type is so it generally needs to use the typedefs Quote: does the object I return have to be (non-const) referencable or can I return a temporary object of typey? If I'm not allowed to, how can I write some vector<bool> uses something that is not bool& and I don't know of any practical drawback. Quote: iterator and especially operator*(), if I have to create its result on the fly? I hope, I made my question understandable. regards, alex Back to top Alexander Stippler Guest Posted: Mon Dec 29, 2003 5:10 pm    Post subject: Re: iterators::reference - what requirements on it are expos Nick Hounsome wrote: Quote: "Alexander Stippler" <stip (AT) mathematik (DOT) uni-ulm.de> wrote in message news:3feeedf6 (AT) news (DOT) uni-ulm.de... Hi, I've got a question concerning iterators. I'm writing some container class and iterators upon it. I have to have typedef typex pointer; typedef typey reference; to be standard conforming. But what semantic requirements does the standard expose on type typey (and typex). If I define reference operator*(), I forget all the details as to why but apparently to be a standard container it turns out that pointer and reference have to be the obvious types (T*, T&) (perhaps const or volatile but not proxy classes). However you don't have to create standard containers and even the standard contains "non-standard" containers in particular vector<bool> precisely because reference isn't bool& and therefore you cannot take the address of one to get bool*. I think I MAY have come across all this in "Effective C++" or "More Effective C++" The main reason to give the typedef is so that standard algorithms can work with your iterators. If an algorith is supplied an iterator it cannot know directly what the fundamental type is so it generally needs to use the typedefs does the object I return have to be (non-const) referencable or can I return a temporary object of typey? If I'm not allowed to, how can I write some vector<bool> uses something that is not bool& and I don't know of any practical drawback. iterator and especially operator*(), if I have to create its result on the fly? I hope, I made my question understandable. regards, alex Indeed both the icc-STL and gcc-STL do not return references for operator*() in some more general places, as I shortly noticed. Look at this, taken from reverse_iterator implementation: reference operator*() const { // return designated value _RanIt _Tmp = current; return (*--_Tmp); } Thanks for your answer. I want to use STL algorithms and that is exactly the extent to which I want to be standard conforming. regards, alex Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ language (comp.lang.c++) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.