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< title > Random Access Traversal Concept< / title >
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< h1 class = "title" > Random Access Traversal Concept< / 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) -->
< p > A class or built-in type < tt class = "docutils literal" > < span class = "pre" > X< / span > < / tt > models the < em > Random Access Traversal< / em >
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concept if the following expressions are valid and respect the stated
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semantics. In the table below, < tt class = "docutils literal" > < span class = "pre" > Distance< / span > < / tt > is
< tt class = "docutils literal" > < span class = "pre" > iterator_traits< X> ::difference_type< / span > < / tt > and < tt class = "docutils literal" > < span class = "pre" > n< / span > < / tt > represents a
constant object of type < tt class = "docutils literal" > < span class = "pre" > Distance< / span > < / tt > .< / p >
< table border = "1" class = "docutils" >
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< colgroup >
< col width = "28%" / >
< col width = "30%" / >
< col width = "23%" / >
< col width = "20%" / >
< / colgroup >
< thead valign = "bottom" >
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< tr > < th class = "head" colspan = "4" > Random Access Traversal Iterator Requirements (in addition to Bidirectional Traversal)< / th >
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< / tr >
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< tr > < th class = "head" > Expression< / th >
< th class = "head" > Return Type< / th >
< th class = "head" > Operational Semantics< / th >
< th class = "head" > Assertion/
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Precondition< / th >
< / tr >
< / thead >
< tbody valign = "top" >
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< tr > < td > < tt class = "docutils literal" > < span class = "pre" > r< / span > < span class = "pre" > +=< / span > < span class = "pre" > n< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > X& < / span > < / tt > < / td >
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< td > < pre class = "first last literal-block" >
{
Distance m = n;
if (m > = 0)
while (m--)
++r;
else
while (m++)
--r;
return r;
}
< / pre >
< / td >
< td > < / td >
< / tr >
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< tr > < td > < tt class = "docutils literal" > < span class = "pre" > a< / span > < span class = "pre" > +< / span > < span class = "pre" > n< / span > < / tt > , < tt class = "docutils literal" > < span class = "pre" > n< / span > < span class = "pre" > +< / span > < span class = "pre" > a< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > X< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > {< / span > < span class = "pre" > X< / span > < span class = "pre" > tmp< / span > < span class = "pre" > =< / span > < span class = "pre" > a;< / span > < span class = "pre" > return< / span > < span class = "pre" > tmp< / span >
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< span class = "pre" > +=< / span > < span class = "pre" > n;< / span > < span class = "pre" > }< / span > < / tt > < / td >
< td > < / td >
< / tr >
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< tr > < td > < tt class = "docutils literal" > < span class = "pre" > r< / span > < span class = "pre" > -=< / span > < span class = "pre" > n< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > X& < / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > return< / span > < span class = "pre" > r< / span > < span class = "pre" > +=< / span > < span class = "pre" > -n< / span > < / tt > < / td >
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< td > < / td >
< / tr >
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< tr > < td > < tt class = "docutils literal" > < span class = "pre" > a< / span > < span class = "pre" > -< / span > < span class = "pre" > n< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > X< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > {< / span > < span class = "pre" > X< / span > < span class = "pre" > tmp< / span > < span class = "pre" > =< / span > < span class = "pre" > a;< / span > < span class = "pre" > return< / span > < span class = "pre" > tmp< / span >
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< span class = "pre" > -=< / span > < span class = "pre" > n;< / span > < span class = "pre" > }< / span > < / tt > < / td >
< td > < / td >
< / tr >
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< tr > < td > < tt class = "docutils literal" > < span class = "pre" > b< / span > < span class = "pre" > -< / span > < span class = "pre" > a< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > Distance< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > a< / span > < span class = "pre" > < < / span > < span class = "pre" > b< / span > < span class = "pre" > ?< / span > < span class = "pre" > distance(a,b)< / span >
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< span class = "pre" > :< / span > < span class = "pre" > -distance(b,a)< / span > < / tt > < / td >
< td > pre: there exists a
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value < tt class = "docutils literal" > < span class = "pre" > n< / span > < / tt > of
< tt class = "docutils literal" > < span class = "pre" > Distance< / span > < / tt > such that
< tt class = "docutils literal" > < span class = "pre" > a< / span > < span class = "pre" > +< / span > < span class = "pre" > n< / span > < span class = "pre" > ==< / span > < span class = "pre" > b< / span > < / tt > . < tt class = "docutils literal" > < span class = "pre" > b< / span >
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< span class = "pre" > ==< / span > < span class = "pre" > a< / span > < span class = "pre" > +< / span > < span class = "pre" > (b< / span > < span class = "pre" > -< / span > < span class = "pre" > a)< / span > < / tt > .< / td >
< / tr >
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< tr > < td > < tt class = "docutils literal" > < span class = "pre" > a[n]< / span > < / tt > < / td >
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< td > convertible to T< / td >
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< td > < tt class = "docutils literal" > < span class = "pre" > *(a< / span > < span class = "pre" > +< / span > < span class = "pre" > n)< / span > < / tt > < / td >
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< td > pre: a is a < em > Readable
Iterator< / em > < / td >
< / tr >
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< tr > < td > < tt class = "docutils literal" > < span class = "pre" > a[n]< / span > < span class = "pre" > =< / span > < span class = "pre" > v< / span > < / tt > < / td >
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< td > convertible to T< / td >
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< td > < tt class = "docutils literal" > < span class = "pre" > *(a< / span > < span class = "pre" > +< / span > < span class = "pre" > n)< / span > < span class = "pre" > =< / span > < span class = "pre" > v< / span > < / tt > < / td >
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< td > pre: a is a < em > Writable
iterator< / em > < / td >
< / tr >
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< tr > < td > < tt class = "docutils literal" > < span class = "pre" > a< / span > < span class = "pre" > < < / span > < span class = "pre" > b< / span > < / tt > < / td >
< td > convertible to < tt class = "docutils literal" > < span class = "pre" > bool< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > b< / span > < span class = "pre" > -< / span > < span class = "pre" > a< / span > < span class = "pre" > > < / span > < span class = "pre" > 0< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > < < / span > < / tt > is a total
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ordering relation< / td >
< / tr >
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< tr > < td > < tt class = "docutils literal" > < span class = "pre" > a< / span > < span class = "pre" > > < / span > < span class = "pre" > b< / span > < / tt > < / td >
< td > convertible to < tt class = "docutils literal" > < span class = "pre" > bool< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > b< / span > < span class = "pre" > < < / span > < span class = "pre" > a< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > > < / span > < / tt > is a total
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ordering relation< / td >
< / tr >
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< tr > < td > < tt class = "docutils literal" > < span class = "pre" > a< / span > < span class = "pre" > > =< / span > < span class = "pre" > b< / span > < / tt > < / td >
< td > convertible to < tt class = "docutils literal" > < span class = "pre" > bool< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > !(a< / span > < span class = "pre" > < < / span > < span class = "pre" > b)< / span > < / tt > < / td >
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< td > < / td >
< / tr >
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< tr > < td > < tt class = "docutils literal" > < span class = "pre" > a< / span > < span class = "pre" > < =< / span > < span class = "pre" > b< / span > < / tt > < / td >
< td > convertible to < tt class = "docutils literal" > < span class = "pre" > bool< / span > < / tt > < / td >
< td > < tt class = "docutils literal" > < span class = "pre" > !(a< / span > < span class = "pre" > > < / span > < span class = "pre" > b)< / span > < / tt > < / td >
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< td > < / td >
< / tr >
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< tr > < td > < tt class = "docutils literal" > < span class = "pre" > iterator_traversal< X> ::type< / span > < / tt > < / td >
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< td > Convertible to
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< tt class = "docutils literal" > < span class = "pre" > random_access_traversal_tag< / span > < / tt > < / td >
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< td > < / td >
< td > < / td >
< / tr >
< / tbody >
< / table >
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