> it would take quite a compiler to prevent the creation of an intermediate string. You could have every function return an iterator over the characters that would end up in the string, iterate over that to check whether the string already is interned, and if not, iterate again to allocate a new string, but I think it would typically be cheaper to create it and let he young generation garbage collector collect it.

I can't think of a language where you would always want to canonicalize strings at a global scope. For example, consider the case where you have a large number of threads and cores. Unless the strings are explicitly allocated on their own cache lines, any thread that references a string now has to worry about false sharing. You would also need to worry about the contention on the canonical store.

At a user level, in languages like Java, there's generally no reason to create any intermediate string if you're already reading from a direct byte buffer. This covers a fairly large set of use cases. There may be other techniques considering Java supports scalar interpolation now, but direct byte buffers have been the most effective in my experience.