Re: User-defined iterator
jddahl@gmail.com wrote:
Object A is composed of a vector of A (itself) and a vector of
B. I'm running into difficulties creating an iterator of all
the Bs (those contained within the vector of As as well as the
vector of Bs.) Somehow I have to maintain the state within the
iterator of which A and which B of that A I'm on, but this
seems to break the recursive nature of "A is composed of As."
As others have pointed out, a type A cannot directly contain an
std::vector< A >. You need some form of indirection. Something
like:
struct A { std::vector<A> nested ; } ;
fails to compile with g++, for example. (With the usual options
for debugging and standard compliance, anyway: g++ -std=c++98
-fno-gnu-keywords -foperator-names -ffor-scope
-D_GLIBCXX_CONCEPT_CHECKS -D_GLIBCXX_DEBUG
-D_GLIBCXX_DEBUG_PEDANTIC. Why doesn't any compiler make the
most useful set of options---the ones you almost always want
when compiling directly from the compile line, rather than
through a makefile/project file or whatever---the defaults?
With either VC++ or g++, I need a good half dozen options for
the "normal" interactive case.)
Beyond that: a recursive algorithm implies a stack of some sort,
so your iterator will require a stack. Which means that it
won't be particularly light weight, and the cost of the constant
copying is likely to kill you. (If you can set a maximum depth
that isn't too deep, you might be able to get by with a C-style
array of A*, which will copy reasonably quickly. For some
definition of reasonable.)
I find that the more I use it, the more I find that while the
STL idiom is acceptable for small, simple things like the
algorithms and containers in the standard library, it doesn't
scale well. (I'm not convinced that there is one idiom that
solves all problems, or that is even usable in all cases.)
--
James Kanze GABI Software
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