1[/ 2 Copyright (c) Vladimir Batov 2009-2016 3 Distributed under the Boost Software License, Version 1.0. 4 See copy at http://www.boost.org/LICENSE_1_0.txt. 5] 6 7[section Default Converter] 8 9[import ../example/default_converter.cpp] 10 11The explicit converter as in 12 13 int i = boost::convert<int>("123", converter).value(); 14 15provides 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`. 16 17[important There is no default converter set by default.] 18 19Consequently, without additional configuration steps the following call will fail to compile: 20 21 int i = boost::convert<int>("123").value(); // No converter provided 22 23However, after `boost::cnv::by_default` is defined simply as: 24 25[default_converter_declaration_simple] 26 27or potentially configured with additional formatting: 28 29[default_converter_declaration_formatted] 30 31the code compiles and deploys `boost::cnv::cstream` when `boost::convert()` is called without an explicitly supplied converter: 32 33[default_converter_example1] 34 35The 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. 36 37[endsect] 38 39