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< title > Transform Iterator< / title >
< meta name = "author" content = "David Abrahams, Jeremy Siek, Thomas Witt" / >
< meta name = "organization" content = "Boost Consulting, Indiana University Open Systems Lab, University of Hanover Institute for Transport Railway Operation and Construction" / >
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< meta name = "date" content = "2006-09-11" / >
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< meta name = "copyright" content = "Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003." / >
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< body >
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< div class = "document" id = "transform-iterator" >
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< h1 class = "title" > Transform Iterator< / h1 >
< table class = "docinfo" frame = "void" rules = "none" >
< col class = "docinfo-name" / >
< col class = "docinfo-content" / >
< tbody valign = "top" >
< tr > < th class = "docinfo-name" > Author:< / th >
< td > David Abrahams, Jeremy Siek, Thomas Witt< / td > < / tr >
< tr > < th class = "docinfo-name" > Contact:< / th >
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< td > < a class = "first reference external" href = "mailto:dave@boost-consulting.com" > dave@ boost-consulting.com< / a > , < a class = "reference external" href = "mailto:jsiek@osl.iu.edu" > jsiek@ osl.iu.edu< / a > , < a class = "last reference external" href = "mailto:witt@ive.uni-hannover.de" > witt@ ive.uni-hannover.de< / a > < / td > < / tr >
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< tr > < th class = "docinfo-name" > Organization:< / th >
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< td > < a class = "first reference external" href = "http://www.boost-consulting.com" > Boost Consulting< / a > , Indiana University < a class = "reference external" href = "http://www.osl.iu.edu" > Open Systems
Lab< / a > , University of Hanover < a class = "last reference external" href = "http://www.ive.uni-hannover.de" > Institute for Transport
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Railway Operation and Construction< / a > < / td > < / tr >
< tr > < th class = "docinfo-name" > Date:< / th >
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< td > 2006-09-11< / td > < / tr >
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< tr > < th class = "docinfo-name" > Copyright:< / th >
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< td > Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003.< / td > < / tr >
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< / tbody >
< / table >
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<!-- Distributed under the Boost -->
<!-- Software License, Version 1.0. (See accompanying -->
<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
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< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > abstract:< / th > < td class = "field-body" > <!-- Copyright David Abrahams 2006. Distributed under the Boost -->
<!-- Software License, Version 1.0. (See accompanying -->
<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
The transform iterator adapts an iterator by modifying the
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< tt class = "docutils literal" > < span class = "pre" > operator*< / span > < / tt > to apply a function object to the result of
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dereferencing the iterator and returning the result.< / td >
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< / tr >
< / tbody >
< / table >
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< div class = "contents topic" id = "table-of-contents" >
< p class = "topic-title first" > Table of Contents< / p >
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< ul class = "simple" >
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< li > < a class = "reference internal" href = "#transform-iterator-synopsis" id = "id2" > < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > synopsis< / a > < / li >
< li > < a class = "reference internal" href = "#transform-iterator-requirements" id = "id3" > < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > requirements< / a > < / li >
< li > < a class = "reference internal" href = "#transform-iterator-models" id = "id4" > < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > models< / a > < / li >
< li > < a class = "reference internal" href = "#transform-iterator-operations" id = "id5" > < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > operations< / a > < / li >
< li > < a class = "reference internal" href = "#example" id = "id6" > Example< / a > < / li >
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< / ul >
< / div >
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< div class = "section" id = "transform-iterator-synopsis" >
< h1 > < a class = "toc-backref" href = "#id2" > < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > synopsis< / a > < / h1 >
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<!-- Copyright David Abrahams 2006. Distributed under the Boost -->
<!-- Software License, Version 1.0. (See accompanying -->
<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
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<!-- Version 1.3 of this document was accepted for TR1 -->
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< pre class = "literal-block" >
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template < class UnaryFunction,
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class Iterator,
class Reference = use_default,
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class Value = use_default>
class transform_iterator
{
public:
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typedef /* see below */ value_type;
typedef /* see below */ reference;
typedef /* see below */ pointer;
typedef iterator_traits< Iterator> ::difference_type difference_type;
typedef /* see below */ iterator_category;
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transform_iterator();
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transform_iterator(Iterator const& x, UnaryFunction f);
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template< class F2, class I2, class R2, class V2>
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transform_iterator(
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transform_iterator< F2, I2, R2, V2> const& t
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, typename enable_if_convertible< I2, Iterator> ::type* = 0 // exposition only
, typename enable_if_convertible< F2, UnaryFunction> ::type* = 0 // exposition only
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);
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UnaryFunction functor() const;
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Iterator const& base() const;
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reference operator*() const;
transform_iterator& operator++();
transform_iterator& operator--();
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private:
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Iterator m_iterator; // exposition only
UnaryFunction m_f; // exposition only
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};
< / pre >
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< p > If < tt class = "docutils literal" > < span class = "pre" > Reference< / span > < / tt > is < tt class = "docutils literal" > < span class = "pre" > use_default< / span > < / tt > then the < tt class = "docutils literal" > < span class = "pre" > reference< / span > < / tt > member of
< tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > is
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< tt class = "docutils literal" > < span class = "pre" > result_of< const UnaryFunction(iterator_traits< Iterator> ::reference)> ::type< / span > < / tt > .
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Otherwise, < tt class = "docutils literal" > < span class = "pre" > reference< / span > < / tt > is < tt class = "docutils literal" > < span class = "pre" > Reference< / span > < / tt > .< / p >
< p > If < tt class = "docutils literal" > < span class = "pre" > Value< / span > < / tt > is < tt class = "docutils literal" > < span class = "pre" > use_default< / span > < / tt > then the < tt class = "docutils literal" > < span class = "pre" > value_type< / span > < / tt > member is
< tt class = "docutils literal" > < span class = "pre" > remove_cv< remove_reference< reference> < / span > < span class = "pre" > > ::type< / span > < / tt > . Otherwise,
< tt class = "docutils literal" > < span class = "pre" > value_type< / span > < / tt > is < tt class = "docutils literal" > < span class = "pre" > Value< / span > < / tt > .< / p >
< p > If < tt class = "docutils literal" > < span class = "pre" > Iterator< / span > < / tt > models Readable Lvalue Iterator and if < tt class = "docutils literal" > < span class = "pre" > Iterator< / span > < / tt >
models Random Access Traversal Iterator, then < tt class = "docutils literal" > < span class = "pre" > iterator_category< / span > < / tt > is
convertible to < tt class = "docutils literal" > < span class = "pre" > random_access_iterator_tag< / span > < / tt > . Otherwise, if
< tt class = "docutils literal" > < span class = "pre" > Iterator< / span > < / tt > models Bidirectional Traversal Iterator, then
< tt class = "docutils literal" > < span class = "pre" > iterator_category< / span > < / tt > is convertible to
< tt class = "docutils literal" > < span class = "pre" > bidirectional_iterator_tag< / span > < / tt > . Otherwise < tt class = "docutils literal" > < span class = "pre" > iterator_category< / span > < / tt > is
convertible to < tt class = "docutils literal" > < span class = "pre" > forward_iterator_tag< / span > < / tt > . If < tt class = "docutils literal" > < span class = "pre" > Iterator< / span > < / tt > does not
model Readable Lvalue Iterator then < tt class = "docutils literal" > < span class = "pre" > iterator_category< / span > < / tt > is
convertible to < tt class = "docutils literal" > < span class = "pre" > input_iterator_tag< / span > < / tt > .< / p >
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< / div >
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< div class = "section" id = "transform-iterator-requirements" >
< h1 > < a class = "toc-backref" href = "#id3" > < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > requirements< / a > < / h1 >
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< p > The type < tt class = "docutils literal" > < span class = "pre" > UnaryFunction< / span > < / tt > must be Assignable, Copy Constructible, and
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the expression < tt class = "docutils literal" > < span class = "pre" > f(*i)< / span > < / tt > must be valid where < tt class = "docutils literal" > < span class = "pre" > f< / span > < / tt > is a const object of
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type < tt class = "docutils literal" > < span class = "pre" > UnaryFunction< / span > < / tt > , < tt class = "docutils literal" > < span class = "pre" > i< / span > < / tt > is an object of type < tt class = "docutils literal" > < span class = "pre" > Iterator< / span > < / tt > , and
where the type of < tt class = "docutils literal" > < span class = "pre" > f(*i)< / span > < / tt > must be
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< tt class = "docutils literal" > < span class = "pre" > result_of< const UnaryFunction(iterator_traits< Iterator> ::reference)> ::type< / span > < / tt > .< / p >
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< p > The argument < tt class = "docutils literal" > < span class = "pre" > Iterator< / span > < / tt > shall model Readable Iterator.< / p >
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< / div >
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< div class = "section" id = "transform-iterator-models" >
< h1 > < a class = "toc-backref" href = "#id4" > < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > models< / a > < / h1 >
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< p > The resulting < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > models the most refined of the
following that is also modeled by < tt class = "docutils literal" > < span class = "pre" > Iterator< / span > < / tt > .< / p >
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< blockquote >
< ul class = "simple" >
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< li > Writable Lvalue Iterator if < tt class = "docutils literal" > < span class = "pre" > transform_iterator::reference< / span > < / tt > is a non-const reference.< / li >
< li > Readable Lvalue Iterator if < tt class = "docutils literal" > < span class = "pre" > transform_iterator::reference< / span > < / tt > is a const reference.< / li >
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< li > Readable Iterator otherwise.< / li >
< / ul >
< / blockquote >
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< p > The < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > models the most refined standard traversal
concept that is modeled by the < tt class = "docutils literal" > < span class = "pre" > Iterator< / span > < / tt > argument.< / p >
< p > If < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > is a model of Readable Lvalue Iterator then
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it models the following original iterator concepts depending on what
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the < tt class = "docutils literal" > < span class = "pre" > Iterator< / span > < / tt > argument models.< / p >
< table border = "1" class = "docutils" >
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< colgroup >
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< col width = "47%" / >
< col width = "53%" / >
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< / colgroup >
< thead valign = "bottom" >
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< tr > < th class = "head" > If < tt class = "docutils literal" > < span class = "pre" > Iterator< / span > < / tt > models< / th >
< th class = "head" > then < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > models< / th >
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< / tr >
< / thead >
< tbody valign = "top" >
< tr > < td > Single Pass Iterator< / td >
< td > Input Iterator< / td >
< / tr >
< tr > < td > Forward Traversal Iterator< / td >
< td > Forward Iterator< / td >
< / tr >
< tr > < td > Bidirectional Traversal Iterator< / td >
< td > Bidirectional Iterator< / td >
< / tr >
< tr > < td > Random Access Traversal Iterator< / td >
< td > Random Access Iterator< / td >
< / tr >
< / tbody >
< / table >
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< p > If < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > models Writable Lvalue Iterator then it is a
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mutable iterator (as defined in the old iterator requirements).< / p >
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< p > < tt class = "docutils literal" > < span class = "pre" > transform_iterator< F1,< / span > < span class = "pre" > X,< / span > < span class = "pre" > R1,< / span > < span class = "pre" > V1> < / span > < / tt > is interoperable with
< tt class = "docutils literal" > < span class = "pre" > transform_iterator< F2,< / span > < span class = "pre" > Y,< / span > < span class = "pre" > R2,< / span > < span class = "pre" > V2> < / span > < / tt > if and only if < tt class = "docutils literal" > < span class = "pre" > X< / span > < / tt > is
interoperable with < tt class = "docutils literal" > < span class = "pre" > Y< / span > < / tt > .< / p >
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< / div >
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< div class = "section" id = "transform-iterator-operations" >
< h1 > < a class = "toc-backref" href = "#id5" > < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > operations< / a > < / h1 >
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< p > In addition to the operations required by the concepts modeled by
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< tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > , < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > provides the following
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operations.< / p >
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< p > < tt class = "docutils literal" > < span class = "pre" > transform_iterator();< / span > < / tt > < / p >
< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > with < tt class = "docutils literal" > < span class = "pre" > m_f< / span > < / tt >
and < tt class = "docutils literal" > < span class = "pre" > m_iterator< / span > < / tt > default constructed.< / td >
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< / tr >
< / tbody >
< / table >
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< p > < tt class = "docutils literal" > < span class = "pre" > transform_iterator(Iterator< / span > < span class = "pre" > const& < / span > < span class = "pre" > x,< / span > < span class = "pre" > UnaryFunction< / span > < span class = "pre" > f);< / span > < / tt > < / p >
< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > with < tt class = "docutils literal" > < span class = "pre" > m_f< / span > < / tt >
initialized to < tt class = "docutils literal" > < span class = "pre" > f< / span > < / tt > and < tt class = "docutils literal" > < span class = "pre" > m_iterator< / span > < / tt > initialized to < tt class = "docutils literal" > < span class = "pre" > x< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
< pre class = "literal-block" >
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template< class F2, class I2, class R2, class V2>
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transform_iterator(
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transform_iterator< F2, I2, R2, V2> const& t
, typename enable_if_convertible< I2, Iterator> ::type* = 0 // exposition only
, typename enable_if_convertible< F2, UnaryFunction> ::type* = 0 // exposition only
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);
< / pre >
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< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "docutils literal" > < span class = "pre" > transform_iterator< / span > < / tt > with < tt class = "docutils literal" > < span class = "pre" > m_f< / span > < / tt >
initialized to < tt class = "docutils literal" > < span class = "pre" > t.functor()< / span > < / tt > and < tt class = "docutils literal" > < span class = "pre" > m_iterator< / span > < / tt > initialized to
< tt class = "docutils literal" > < span class = "pre" > t.base()< / span > < / tt > .< / td >
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< / tr >
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< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > < tt class = "docutils literal" > < span class = "pre" > OtherIterator< / span > < / tt > is implicitly convertible to < tt class = "docutils literal" > < span class = "pre" > Iterator< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
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< p > < tt class = "docutils literal" > < span class = "pre" > UnaryFunction< / span > < span class = "pre" > functor()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "docutils literal" > < span class = "pre" > m_f< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
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< p > < tt class = "docutils literal" > < span class = "pre" > Iterator< / span > < span class = "pre" > const& < / span > < span class = "pre" > base()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "docutils literal" > < span class = "pre" > m_iterator< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
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< p > < tt class = "docutils literal" > < span class = "pre" > reference< / span > < span class = "pre" > operator*()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "docutils literal" > < span class = "pre" > m_f(*m_iterator)< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
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< p > < tt class = "docutils literal" > < span class = "pre" > transform_iterator& < / span > < span class = "pre" > operator++();< / span > < / tt > < / p >
< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "docutils literal" > < span class = "pre" > ++m_iterator< / span > < / tt > < / td >
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< / tr >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "docutils literal" > < span class = "pre" > *this< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
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< p > < tt class = "docutils literal" > < span class = "pre" > transform_iterator& < / span > < span class = "pre" > operator--();< / span > < / tt > < / p >
< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "docutils literal" > < span class = "pre" > --m_iterator< / span > < / tt > < / td >
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< / tr >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "docutils literal" > < span class = "pre" > *this< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
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<!-- Copyright David Abrahams 2006. Distributed under the Boost -->
<!-- Software License, Version 1.0. (See accompanying -->
<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
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< pre class = "literal-block" >
template < class UnaryFunction, class Iterator>
transform_iterator< UnaryFunction, Iterator>
make_transform_iterator(Iterator it, UnaryFunction fun);
< / pre >
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< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "docutils literal" > < span class = "pre" > transform_iterator< UnaryFunction,< / span > < span class = "pre" > Iterator> < / span > < / tt > with < tt class = "docutils literal" > < span class = "pre" > m_f< / span > < / tt >
initialized to < tt class = "docutils literal" > < span class = "pre" > f< / span > < / tt > and < tt class = "docutils literal" > < span class = "pre" > m_iterator< / span > < / tt > initialized to < tt class = "docutils literal" > < span class = "pre" > x< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
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< pre class = "literal-block" >
template < class UnaryFunction, class Iterator>
transform_iterator< UnaryFunction, Iterator>
make_transform_iterator(Iterator it);
< / pre >
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< table class = "docutils field-list" frame = "void" rules = "none" >
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< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "docutils literal" > < span class = "pre" > transform_iterator< UnaryFunction,< / span > < span class = "pre" > Iterator> < / span > < / tt > with < tt class = "docutils literal" > < span class = "pre" > m_f< / span > < / tt >
default constructed and < tt class = "docutils literal" > < span class = "pre" > m_iterator< / span > < / tt > initialized to < tt class = "docutils literal" > < span class = "pre" > x< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
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<!-- Copyright David Abrahams 2006. Distributed under the Boost -->
<!-- Software License, Version 1.0. (See accompanying -->
<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
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< / div >
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< div class = "section" id = "example" >
< h1 > < a class = "toc-backref" href = "#id6" > Example< / a > < / h1 >
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< p > This is a simple example of using the transform_iterators class to
generate iterators that multiply (or add to) the value returned by
dereferencing the iterator. It would be cooler to use lambda library
in this example.< / p >
< pre class = "literal-block" >
int x[] = { 1, 2, 3, 4, 5, 6, 7, 8 };
const int N = sizeof(x)/sizeof(int);
typedef boost::binder1st< std::multiplies< int> > Function;
typedef boost::transform_iterator< Function, int*> doubling_iterator;
doubling_iterator i(x, boost::bind1st(std::multiplies< int> (), 2)),
i_end(x + N, boost::bind1st(std::multiplies< int> (), 2));
std::cout < < " multiplying the array by 2:" < < std::endl;
while (i != i_end)
std::cout < < *i++ < < " " ;
std::cout < < std::endl;
std::cout < < " adding 4 to each element in the array:" < < std::endl;
std::copy(boost::make_transform_iterator(x, boost::bind1st(std::plus< int> (), 4)),
boost::make_transform_iterator(x + N, boost::bind1st(std::plus< int> (), 4)),
std::ostream_iterator< int> (std::cout, " " ));
std::cout < < std::endl;
< / pre >
< p > The output is:< / p >
< pre class = "literal-block" >
multiplying the array by 2:
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2 4 6 8 10 12 14 16
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adding 4 to each element in the array:
5 6 7 8 9 10 11 12
< / pre >
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< p > The source code for this example can be found < a class = "reference external" href = "../example/transform_iterator_example.cpp" > here< / a > .< / p >
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< / div >
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< / div >
< div class = "footer" >
< hr class = "footer" / >
< a class = "reference external" href = "transform_iterator.rst" > View document source< / a > .
Generated by < a class = "reference external" href = "http://docutils.sourceforge.net/" > Docutils< / a > from < a class = "reference external" href = "http://docutils.sourceforge.net/rst.html" > reStructuredText< / a > source.
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< / div >
< / body >
< / html >
