Immutable string

In some code bases strings are (1) often created from string literals, (2) never modified after being created, and (3) copied multiple times. For code bases like that, std::string is actually sub-optimal. Creating an std::string from a literal must heap-allocate a copy because std::string is mutable. When you copy an std::string object another heap-allocation has to be made because the standard does not allow std::string to use copy-on-write semantics.

If you don't need the mutability, this library provides a better option: an immutable string with (mostly) the same interface as std::string.

Since individual characters are immutable, string literals can be referenced instead of copied:

#include <tj/string.hpp>
#include <iostream>

int main()
{
    // you _must_ use the user-defined literal to avoid memory allocation
    using namespace tj::literals;
    // no memory allocated by tj::string here
    const auto s = "hello"_is;
    std::cout << s << '\n;
}

Similarly copying a string object just bumps the reference count on the allocated buffer:

#include <tj/string.hpp>
#include <iostream>

int main()
{
    const tj::string s1 = "hello, world";
    // no additional memory allocated by tj::string here
    const tj::string s2 = s1;
    std::cout << s2 << '\n;
}

Even though you cannot modify the string, e.g. change individual characters or the length of the string, you can still assign a new value to immutable string objects:

#include <tj/string.hpp>
#include <iostream>

int main()
{
    using namespace tj::literals;
    auto s = "hello"_is;
    s = "goodbye";
    std::cout << s << '\n;
}