Struct template with_default

Boost C++ Libraries

Struct template with_default

boost::taar::handler::with_default — Wrap an argument provider with a fallback value.

Synopsis

// In header: <boost/taar/handler/rest_arg.hpp>

template<typename ArgProviderType, typename ValueType> 
struct with_default {
  // types
  typedef ArgProviderType arg_provider_type;        
  typedef ValueType       value_type;               
  typedef unspecified     arg_provider_request_type;
  typedef unspecified     arg_provider_result_type; 

  // public member functions
  with_default(arg_provider_type, value_type);
  std::string name() const;
  std::string description() const;
  decltype(auto) 
  operator()(arg_provider_request_type const &, matcher::context const &) const;
  value_type const & default_value() const;

  // public data members
  arg_provider_type arg_provider_;
  value_type default_value_;
};

Description

When the wrapped provider fails with error::argument_not_found, default_value is substituted instead. Other errors are propagated unchanged. This is the idiomatic way to make an argument optional with a non-std::optional type.

taar::handler::rest(
    [](int page) { ... },
    taar::handler::with_default(taar::handler::query_arg("page"), 1));

`with_default` public member functions

with_default(arg_provider_type arg_provider, value_type default_value);

```
std::string name() const;
```
```
std::string description() const;
```

decltype(auto) 
operator()(arg_provider_request_type const & request, 
           matcher::context const & context) const;

value_type const & default_value() const;