Differences between boost::string_ref and boost::string_view

Question

Boost provides two different implementations of string_view, which will be a part of C++17:

• boost::string_ref in utility/string_ref

Answer 1

Funnily enough right now I'm at the ACCU conference with Marshall Clow (the force behind string_view et al on the committee) and I was quite literally about to ask him at the bar earlier today before I was called away about his views on string_view versus Bjarne's Guideline Support Library (GSL) gsl::span which is a very similar thing (gsl-lite is my personal favourite implementation of the GSL as it's 03 compatible, but there are many others). I had heard they were to be unified into a single implementation for standardisation, and the gsl::span direction is to be the future, but I'll report back here from the horse's mouth himself if I'm wrong on that. For now, assume the gsl::span direction is the current future and Boost will get updated to have something similar soon, even if using string_view = gsl::span is essentially string_view.

Edit: I just spoke to Marshall downstairs. He tells me that string_view, as per the implementation in Boost, is definitely in C++ 17. array_view is not, nor is anything historically surrounding string_view for now.

The GSL string_span is a separate entity not expected to enter in C++ 17, nor are there any present plans to unify the implementations as they solve different use cases, specifically that string_view is always a constant view of the borrowed character array, whereas string_span is expected to be a potentially modifiable view of the borrowed character array with potential uses as a source for construction of new strings, so string_span might perhaps eventually become a generalisation of string_view in some future C++ standard.