Overview

C++98 immutable string class that provides functionality of both std::string and std::string_view.

The main purpose of const_string is to allow functions that take/return immutable strings (most of functions) to use only const_string for all kinds of strings and not require memory allocation.

The class is called const_string because it doesn't allow modification of individual characters of the string. This restriction allows for cheap copying with thread-safe reference counting. The library is inteded for inclusion into boost library, but lacks documentation required for library acceptance review.

GNU C++98 std::string was reference-counted, but a C++ standard compliant std::string cannot be both reference-counted and fully standard compliant, so that GNU C++11 std::string is no longer reference-counted. The mutability of individual characters of std::string is the main reason it cannot be reference-counted.

const_string doesn't allow modification of individual characters in order to provide cheap/shallow copies and also provides std::string_view functionality to allow for no memory allocation usage.

Main features

• Optional memory allocation, unlike functions taking std::string argument.
• No extra overloads for std::string_view to avoid std::string memory allocation.
• Customizable small string optimization buffer size. On a 64-bit platform, the minimum size of a const_string is 16 bytes, which allows for 8-byte small string optimization. The small string buffer size is controlled by the template argument, should you need to change the default.
• Longer strings are reference-counted, so that copies are cheap and thread-safe.

Examples

using boost::const_string;

// No memory allocation due to small string optimization.
const_string a("abc");

// Memory allocation because the string is long.
const_string b0("abcdefghijklmnoprstqvwxyz"); 

// No memory allocation, reference counter increment.
const_string b1 = b0; 

// No memory allocation, the string literal is referred to.
// Equivalent to using std::string_view.
const_string c(boost::cref("abcdefghijklmnoprstqvwxyz")); 

// Refer to std::string with no memory allocation or copy.
// Equivalent to using std::string_view.
std::string d0("abcdefghijklmnoprstqvwxyz");
const_string d1(boost::cref(d0)); 

TODO

• Documentation.
• Update with C++11.
• Use Facebook small string optimization to allow for 7 more characters with no memory allocation.