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POHow to reference an optional submatch inside a semantic action with boost::xpressive static?
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  1. POHow to reference an optional submatch inside a semantic action with boost::xpressive static?
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    copied!<p>I have a boost xpressive sregex and semantic action that is equivalent to the following:</p> <pre><code>Rule = ('[' &gt;&gt; (s1=!(set=')',']','&gt;')))[some_op(as&lt;std::string&gt;(s1))]; </code></pre> <p>Previously I was using this on boost 1.43 without any problems. I have had to upgrade to a newer boost recently and now I run into the following issue. On boost 1.48 when the submatch does not match anything (as it is optional) a <code>bad_lexical_cast</code> exception is thrown by the semantic action when <code>as</code> executes on the empty <code>s1</code> object.</p> <p>How can I fix this problem, is it just a coincidence that it worked before and there is some better safer way I should be using to do this? Or is this just e.g. some change in the <code>lexical_cast</code> code that now breaks <code>xpressive</code>?</p> <h1>Additional information</h1> <p>I have managed to temporarily solve the actual problem by changing the following in regex_actions.hpp:</p> <pre><code>template&lt;typename T&gt; struct as { BOOST_PROTO_CALLABLE() typedef T result_type; template&lt;typename Value&gt; T operator()(Value const &amp;val) const { return lexical_cast&lt;T&gt;(val); } }; </code></pre> <p>Into:</p> <pre><code>template&lt;typename T&gt; struct as { BOOST_PROTO_CALLABLE() typedef T result_type; template&lt;typename Value&gt; T operator()(Value const &amp;val) const { if(val.first==val.second) { return T(); } else { return lexical_cast&lt;T&gt;(val); } } }; </code></pre> <p>This leads me to believe that perhaps this is something that needs to be fixed in <code>xpressive</code> itself. However I am not 100% convinced yet that it's not something I am doing wrong on my side, anyone with a bit more knowledge on <code>xpressive</code> have some insight into this?</p>
 

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