EQ2EMu/EQ2/source/depends/boost_1_72_0/libs/convert/doc/default_converter.qbk

[/
  Copyright (c) Vladimir Batov 2009-2016
  Distributed under the Boost Software License, Version 1.0.
  See copy at http://www.boost.org/LICENSE_1_0.txt.
]

[section Default Converter]

[import ../example/default_converter.cpp]

The explicit converter as in

 int i = boost::convert<int>("123", converter).value();
 
provides considerable flexibility, configurability and efficiency. However, in certain contexts that might be not that important or even counter-productive if, for example, an application relies on certain consistent behavior associated with one particular converter type and configuration. To accommodate such a scenario ['Boost.Convert] introduces the concept of the ['default converter] implemented as  `boost::cnv::by_default`. 

[important There is no default converter set by default.] 

Consequently, without additional configuration steps the following call will fail to compile: 

 int i = boost::convert<int>("123").value(); // No converter provided
 
However, after `boost::cnv::by_default` is defined simply as:

[default_converter_declaration_simple]

or potentially configured with additional formatting:

[default_converter_declaration_formatted]

the code compiles and deploys `boost::cnv::cstream` when `boost::convert()` is called without an explicitly supplied converter:

[default_converter_example1]

The trade-off for the convenience is the rigid converter configuration (which in certain contexts might be the desired behavior) and a potential performance impact. When a converter is not provided explicitly, the default converter is created, potentially configured, deployed and destroyed for every `boost::convert()` call. Consequently, if efficiency of this particular component is important, then the implementation of `boost::cnv::by_default` will need to take that into account and to make sure those operations are cheap.

[endsect]