## Class has_attribute<void>

boost::log::expressions::has_attribute<void>

## Synopsis

    // In header: <boost/log/expressions/predicates/has_attr.hpp>

    class has_attribute<void> {
    public:
      // types
      typedef bool result_type;  // Function result_type.
      typedef void value_type;   // Expected attribute value type.

      // construct/copy/destruct
      explicit has_attribute(attribute_name const &);

      // public member functions
      result_type operator()(attribute_value_set const &) const;
      result_type operator()(boost::log::record_view const &) const;
    };

## Description

An attribute value presence checker. This specialization does not check the type of the attribute value.

### `has_attribute` public construct/copy/destruct

1.     explicit has_attribute(attribute_name const & name);

   Initializing constructor

   Parameters: |
   `name` | Attribute name

### `has_attribute` public member functions

1.     result_type operator()(attribute_value_set const & attrs) const;

   Checking operator

   Parameters: |
   `attrs` | A set of attribute values
   Returns: | `true` if the log record contains the sought attribute value, `false` otherwise

2.     result_type operator()(boost::log::record_view const & rec) const;

   Checking operator

   Parameters: |
   `rec` | A log record
   Returns: | `true` if the log record contains the sought attribute value, `false` otherwise