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## Struct pop_front

boost::proto::functional::pop_front — A PolymorphicFunctionObject type that invokes the `fusion::pop_front()` algorithm on its argument.

## Synopsis

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

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

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

## Description

A PolymorphicFunctionObject type that invokes the `fusion::pop_front()` algorithm on its argument. This is useful for defining a CallableTransform such as `pop_front(_)`, which removes the first child from a Proto expression node. Such a transform might be used as the first argument to the `proto::fold<>` transform; that is, fold all but the first child.

### `pop_front` public member functions

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

   Returns: | `fusion::pop_front(expr)`

2.     template<typename Expr>
         typename fusion::result_of::pop_front< Expr const >::type
         operator()(Expr const & expr) const;

   Returns: | `fusion::pop_front(expr)`