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  1. /*
  2. I'm playing around with Boost Variant in order to create a tree made out of nodes
  3. that can either be a value (leaf), or a set of one or two children
  4.  
  5. The problem is that nesting doesn't work for a single child case - I have wrong depth here
  6.  
  7. */
  8.  
  9. #define BOOST_VARIANT_NO_FULL_RECURSIVE_VARIANT_SUPPORT
  10. #include <boost/variant.hpp>
  11.  
  12. #include <iostream>
  13. #include <typeinfo>
  14.  
  15. typedef boost::make_recursive_variant<
  16. 	// can be one of
  17.     int,
  18.     bool,
  19.     boost::recursive_variant_, // single child
  20.     std::pair<boost::recursive_variant_, boost::recursive_variant_> // two children
  21. >::type Node;
  22.  
  23. struct TreePrint : public boost::static_visitor<void> {
  24.     mutable int depth;
  25.     template <typename T>
  26.     void operator()(const T& value) const {
  27.         depth++;
  28.         std::cout << "[depth " << depth << "]: "  << value << std::endl;
  29.         depth--;
  30.     }
  31.  
  32.     void operator()(const Node& value) const {
  33.         depth++;
  34.         boost::apply_visitor(*this, value);
  35.         depth--;
  36.     }
  37.  
  38.     void operator()(const std::pair<Node, Node>& value) const {
  39.         depth++;
  40.         boost::apply_visitor(*this, value.first);
  41.         boost::apply_visitor(*this, value.second);
  42.         depth--;
  43.     }
  44. };
  45.  
  46. int main() {
  47.     /*
  48.         root
  49.         /  \
  50.        i1  i2
  51.       /  \   \ 
  52.      t1   5  t1
  53.     /  \       \
  54.    1  true     10  
  55.  
  56.     */
  57.  
  58.     Node root(
  59.         std::pair<Node, Node>(
  60.             std::pair<Node, Node>( // i1
  61.                 std::pair<Node, Node>( // t1
  62.                     1,
  63.                     true
  64.                 ),
  65.                 5
  66.             ),
  67.             Node( // i2
  68.                 Node( // t1
  69.                     Node(10) // ERROR - should have depth 4
  70.                 )
  71.             )
  72.         )
  73.     );
  74.  
  75.     boost::apply_visitor(TreePrint(), root );
  76. }
Success #stdin #stdout 0s 3436KB
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Standard input is empty
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[depth 4]: 1
[depth 4]: 1
[depth 3]: 5
[depth 2]: 10
https://ideone.com/B096YJ
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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