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Added a mention of the pair_generator; updated conclusion to stress Policy Adaptor.

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[SVN r11039]
This commit is contained in:
Dave Abrahams
2001-09-05 18:33:04 +00:00
parent d41013d9dc
commit e7592e5f83
1 changed files with 33 additions and 8 deletions
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tmpw2001-paper/iter-adaptor.tex
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@@ -211,8 +211,8 @@ iterator types from scratch), but a generalized iterator
\emph{adaptor} is even more useful. An adaptor generator allows one to \emph{adaptor} is even more useful. An adaptor generator allows one to
build whole families of iterator instances based on existing build whole families of iterator instances based on existing
iterators. In the Boost Iterator Adaptor Library, the iterators. In the Boost Iterator Adaptor Library, the
\iteratoradaptor\ class template plays the roles of both an iterator \iteratoradaptor\ class template plays the roles of both iterator
generator and an iterator adaptor generator. The behaviors of generator and iterator adaptor generator. The behaviors of
\iteratoradaptor{} instances are supplied through a policies \iteratoradaptor{} instances are supplied through a policies
class~\cite{alexandrescu01:_modern_cpp_design} which allows class~\cite{alexandrescu01:_modern_cpp_design} which allows
users to specialize adaptation. Users go beyond generating new users to specialize adaptation. Users go beyond generating new
@@ -883,7 +883,7 @@ list using a template meta-program utility class named
\end{verbatim} \end{verbatim}
} }
\noindent So, for example, to retrieve the argument for the \noindent For example, to retrieve the argument for the
\valuetype\ we write the following: \valuetype\ we write the following:
{\footnotesize {\footnotesize
@@ -986,6 +986,32 @@ templates (as shown in the previous Subsection). This allows the same
function template to provide the implementation of all the function template to provide the implementation of all the
combinations of constant and mutable iterator interaction. combinations of constant and mutable iterator interaction.
Many of the specialized adaptors in the Boost Iterator Adaptor Library supply an
additional type generator (as described in \S\ref{sec:iter-type-generator}) for
matched pairs of constant and mutable iterators. For example, an ``indirect
container'' using a matched pair of indirect iterators might be declared as
follows:
% jeremy, I didn't want to do this, but it was breaking this tiny example
% across pages. Do you know a better way to stop that?
% \newpage\
% when I added this, it broke an example at the end of the next page across
% pages, so I just bailed.
{\footnotesize
\begin{verbatim}
template <class BaseContainer>
struct indirect
{
typedef typename BaseContainer::iterator base_iterator;
typedef indirect_iterator_pair_generator<base_iterator> iterator_generator;
typedef typename iterator_generator::iterator iterator;
typedef typename iterator_generator::const_iterator const_iterator;
...
};
\end{verbatim}
}
\subsection{Redundant Operators} \subsection{Redundant Operators}
@@ -1181,11 +1207,10 @@ policies class) for the iterator, and then the
\iteratoradaptor\ takes care of most of the implementation \iteratoradaptor\ takes care of most of the implementation
details. details.
Taking a step back, the design approach was to create a canonical Taking a step back, the Policy Adaptor design pattern allowed us to easily
implementation of a concept (iterator) and then delegate the core produce both new models of the iterator concept, and new iterator adaptors. This
implementation issues to a policies class. This approach can be strategy can be applied in situations where there is large family of components
applied in situations where there is large family of components that that share the same interface. For example, we plan on applying this design
share the same interface. For example, we plan on applying this design
approach to containers and algebraic types. approach to containers and algebraic types.
\bibliographystyle{abbrv} \bibliographystyle{abbrv}