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## Struct deep_copy

boost::proto::functional::deep_copy — A PolymorphicFunctionObject type for deep-copying Proto expression trees.

## Synopsis

    // In header: <boost/proto/deep_copy.hpp>

    struct deep_copy :  proto::callable {
      // member classes/structs/unions
      template<typename This, typename Expr>
      struct result<This(Expr)> :  result_of::deep_copy<Expr> {
      };

      // public member functions
      template<typename Expr>
        result_of::deep_copy<Expr>::type operator()(Expr const &) const;
    };

## Description

A PolymorphicFunctionObject type for deep-copying Proto expression trees. When a tree is deep-copied, all internal nodes and terminals held by reference are instead held by value. The only exception is function references, which continue to be held by reference.

### `deep_copy` public member functions

1.     template<typename Expr>
         result_of::deep_copy<Expr>::type operator()(Expr const & expr) const;

   Deep-copies a Proto expression tree, turning all nodes and terminals held by reference into ones held by value.