boost/libs/convert/doc/no_optional_interface.qbk

[/
  Copyright (c) Vladimir Batov 2009-2020
  Distributed under the Boost Software License, Version 1.0.
  See copy at http://www.boost.org/LICENSE_1_0.txt.
]

[section Alternative Interface]

[:[*['"It's not a question of happiness, it's a requirement. Consider the alternative” Doug Horton]]]

As it was indicated previously [@boost:/libs/optional/index.html `boost::optional`] is the actual type returned by the `boost::convert()` main interface:

 boost::optional<TypeOut> boost::convert(TypeIn const&, Converter const&);

The signature is ['functionally-complete] and routinely elided during compilation. Still, the following alternative (and arguably more traditional) interface might be potentially more suitable for certain deployment scenarios (or due to personal preferences):

 TypeOut convert(TypeIn const&, Converter const&, TypeOut const& fallback_value);
 TypeOut convert(TypeIn const&, Converter const&, Functor const& fallback_func);
 TypeOut convert(TypeIn const&, Converter const&, boost::throw_on_failure);

The interface still provides unambiguous behavior and readability, full support for various program flows and various degrees of conversion-failure detection and processing. It can be deployed in a similar fashion as follows:

[getting_serious_example5]
[getting_serious_example7]

Still, the described interfaces are convenience wrappers around the main interface which provides the described behavior with:

[getting_serious_example8]

[endsect] [/section Return Value]