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POWhy can't I use a boost::function in an Objective-C++ block?
 

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  1. POWhy can't I use a boost::function in an Objective-C++ block?
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    <p>The following code throws an exception</p> <pre><code>terminate called after throwing an instance of 'boost::exception_detail::clone_impl&lt;boost::exception_detail::error_info_injector&lt;boost::bad_function_call&gt; &gt;' what(): call to empty boost::function </code></pre> <p>at the line <code>f()</code> (while executing the block):</p> <pre><code>void foo(); // assume this is defined somewhere boost::function&lt;void()&gt; f = boost::bind(&amp;foo); ^(void) { f(); }(); </code></pre> <p>However, according to <a href="http://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/Blocks/Blocks.pdf" rel="nofollow">the documentation on blocks</a>,</p> <blockquote> <p>In general you can use C++ objects within a block. Within a member function, references to member variables and functions are via an implicitly imported this pointer and thus appear mutable. There are two considerations that apply if a block is copied:</p> <ul> <li><p>If you have a __block storage class for what would have been a stack-based C++ object, then the usual copy constructor is used.</p></li> <li><p>If you use any other C++ stack-based object from within a block, it must have a const copy constructor. The C++ object is then copied using that constructor.</p></li> </ul> </blockquote> <p>This seems to be true normally; if I replace <code>f</code> above with an instance of a simple class with an <code>operator()()</code>, the above code runs as expected.</p> <p>Why doesn't the version with <code>boost::function</code> work?</p>
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    1. USJesse Beder
    1. USJesse Beder
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      1. VTUpMod
    1. COI'm no boost expert, but I'd hazard a guess that it relates to the *const copy constructor* for the `boost::function<>` type (per the quoted documentation).
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      1. USRichard
    2. CODo you get the same error without the bind call (not needed for free functions, see [here](http://www.boost.org/doc/libs/1_46_1/doc/html/function/tutorial.html#id1274976))? What about using the portable syntax, function0<> instead of function<>?
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      1. POWhy can't I use a boost::function in an Objective-C++ block?
      1. USacademicRobot
    3. COI'm curious about the `bind()` call as well, unneeded and could be responsible for the error.
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      1. USlefticus
 

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