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## Struct eval

boost::proto::functional::eval — A PolymorphicFunctionObject type for evaluating a given Proto expression with a given context.

## Synopsis

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

    struct eval :  proto::callable {
      // member classes/structs/unions
      template<typename This, typename Expr, typename Context>
      struct result<This(Expr, Context)> :
        proto::result_of::eval<
          typename boost::remove_reference< Expr >::type,
          typename boost::remove_reference< Context >::type
        >
      {
      };

      // public member functions
      template<typename Expr, typename Context>
        typename proto::result_of::eval< Expr, Context >::type
        operator()(Expr &, Context &) const;
      template<typename Expr, typename Context>
        typename proto::result_of::eval< Expr, Context >::type
        operator()(Expr &, Context const &) const;
    };

## Description

### `eval` public member functions

1.     template<typename Expr, typename Context>
         typename proto::result_of::eval< Expr, Context >::type
         operator()(Expr & expr, Context & context) const;

   Evaluate a given Proto expression with a given context.

   Parameters: |
   `context` | The context in which the expression should be evaluated.
   `expr` | The Proto expression to evaluate.
   Returns: | `typename Context::template eval<Expr>()(expr, context)`

2.     template<typename Expr, typename Context>
         typename proto::result_of::eval< Expr, Context >::type
         operator()(Expr & expr, Context const & context) const;

   This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.