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POHow to use a phoenix expression with boost::transform_iterator?
 

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  1. POHow to use a phoenix expression with boost::transform_iterator?
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    <p><strong>&lt;Update&gt;</strong> As usual for me, the question was a wrong one. The actual question is: why doesn't transform_iterator use the conventional result_of&lt;> metafunction to determine the return type, instead of accessing UnaryFunc::result_type directly. Posted an answer with a work around. <strong>&lt;/Update&gt;</strong></p> <p>Specifically, is there a way to make a phoenix expression expose a <code>result_type</code> type as expected for the std::unary_function concept? boost::transform_iterator seems to expect this, and from looking at the src of it, I don't see a simple work around. </p> <p>Here's some code that reproduces the problem I've been having:</p> <pre><code>#include &lt;boost/iterator/transform_iterator.hpp&gt; #include &lt;boost/spirit/home/phoenix.hpp&gt; #include &lt;numeric&gt; #include &lt;iostream&gt; using namespace boost::phoenix; using namespace boost::phoenix::arg_names; int main(void){ int i[] = {4,2,5,3}; std::cout &lt;&lt; std::accumulate( boost::make_transform_iterator(i, _1*_1), boost::make_transform_iterator(i+4, _1*_1), 0 ) &lt;&lt; std::endl; return 0; } </code></pre> <p>The relavent portion of the error message from compiling this is (gcc 4.3.4, boost 1.43):</p> <pre><code>/usr/include/boost/iterator/transform_iterator.hpp:43: error: no type named ‘result_type’ in ‘struct boost::phoenix::actor&lt;... </code></pre> <p>I have the same problem with boost::lambda (missing <code>result_type</code>). I thought that I had seen similar usage for make_transform_iterator and lambda in the past, now I'm wondering if I just imagined it.</p> <p>Is there a provided wrapper or some other mechanism in phoenix or lambda to expose <code>result_type</code>? </p>
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