## Class template constant

boost::log::attributes::constant — A class of an attribute that holds a single constant value.

## Synopsis

    // In header: <boost/log/attributes/constant.hpp>

    template<typename T>
    class constant : public attribute {
    public:
      // types
      typedef T value_type;  // Attribute value type.

      // member classes/structs/unions

      // Factory implementation.

      class impl : public attribute_value_impl< value_type > {
      public:
        // construct/copy/destruct
        explicit impl(value_type const &);
        explicit impl(value_type &&);
      };

      // construct/copy/destruct
      explicit constant(value_type const &);
      explicit constant(value_type &&);
      explicit constant(cast_source const &);

      // public member functions
      value_type const & get() const;
    };

## Description

The constant is a simplest and one of the most frequently used types of attributes. It stores a constant value, which it eventually returns as its value each time requested.

### `constant` public construct/copy/destruct

1.     explicit constant(value_type const & value);

   Constructor with the stored value initialization

2.     explicit constant(value_type && value);

   Constructor with the stored value initialization

3.     explicit constant(cast_source const & source);

   Constructor for casting support

### `constant` public member functions

1.     value_type const & get() const;

   Returns: | Reference to the contained value.