Struct template fallback_to_default

boost::log::fallback_to_default

Synopsis

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

template<typename DefaultT> 
struct fallback_to_default {
  // types
  typedef remove_cv< typenameremove_reference< DefaultT >::type >::type default_type;  // Default value type. 

  enum { guaranteed_result = true };

  // public member functions
  fallback_to_default();
  explicit fallback_to_default(default_type const &);
  template<typename FunT> bool apply_default(FunT &) const;
  template<typename FunT> bool apply_default(FunT const &) const;

  // public static functions
  static void on_invalid_type(typeindex::type_index const &);
  static void on_missing_value();
};

Description

The fallback_to_default policy results in a default value if the attribute value cannot be extracted.

`fallback_to_default` public member functions

```
fallback_to_default();
```
Default constructor.

explicit fallback_to_default(default_type const & def_val);

Initializing constructor.

```
template<typename FunT> bool apply_default(FunT & fun) const;
```
The method is called in order to apply a function object to the default value.
```
template<typename FunT> bool apply_default(FunT const & fun) const;
```
The method is called in order to apply a function object to the default value.

`fallback_to_default` public static functions

```
static void on_invalid_type(typeindex::type_index const &);
```
The method is called when value extraction failed because the attribute value has different type than requested.
```
static void on_missing_value();
```
The method is called when value extraction failed because the attribute value was not found.

Boost C++ Libraries

Struct template fallback_to_default

Synopsis

Description

fallback_to_default public member functions

fallback_to_default public static functions

`fallback_to_default` public member functions

`fallback_to_default` public static functions