When designing a library it is always a problem to find a balance between generalization and usability. A generic utility can have a wider range of usage with more options for extensibility, but it can also bring unwanted complexity for everyday usage. Imagine a library for drawing geometric objects. It can contain one generic function draw() with many parameters specifying what to draw, like size, number of edges, shape etc. This would allow you to draw almost anything, but usually a user only needs to draw only a triangle or a square and she will have to specify this simple request in a very complicated way.For this purpose two functions, draw_triangle() and draw_square(), would suit much better then a generic draw() function. The String Algorithm Library solves this problem by dividing the interface into two layers. The first layer (defined in the namespace boost) contains ready to use algorithms specialized for common tasks. They are provided in multiple variants to better suit specific needs. The second layer (defined in the namespace boost::string_algo), provides generic interfaces with more options for extending and tunning. For instance, a boost::trim() algorithm trims spaces from an input string. When there is a need to trim something else, there is boost::string_algo::trim() which interface allows one to specify a predicate which selects the characters to be removed.

Locales have a very close relation to string processing. They contain information about the character sets and are used, for example, to change the case of characters and to classify the characters. C++ allows to work with multiple different instances of locales at once. If an algorithm manipulates some data in a way that requires the usage of locales, there must be a way to specify them. However, one instance of locales is sufficient for most of the applications, and for a user it could be very tedious to specify which locales to use on every place where it is needed. Fortunately, the C++ standard allows to specify the global locales (using static member function std:locale::global()). When instantiating an std::locale class without explicit information, the instance will be initialized with the global locale. It means, that if an algorithm needs a locale, it should have an std::locale parameter with default value std::locale(). If a user needs to specify locales explicitly, she can do so. Otherwise the global locales are used.

Regular expressions are an essential part of text processing. For this reason, the library provides also regex variants of some algorithms. The library does not try to replace Boost.Regex, but it merely wraps its functionality in a new interface. As a part of this library regex algorithms integrate smoothly with other components which brings additional value.