Add support for switching to nonstd::string_view

[xiaozhuai]

I currently use c++11 for my project. There is no string_view support.
I've change all std::string_view to nonstd::string_view and works well.
I wonder if we can add this feature to inja, simply enable it by a macro.
Then inja can support c++11 as well.

https://github.com/martinmoene/string-view-lite

[pantor]

Inja 3.3 supports and includes this std::string_view polyfill, but it was removed recently from the master branch as we assume C++17 going forward. I think this is reasonable for "modern" C++ in mid 2022.

What is holding you back at C++11?

[xiaozhuai]

@pantor Thanks for your reply.
An old project holding me back at c++11 : (
And there is no plan to upgrade to c++17.
Old device, old compiler and old c++ runtime library......
I agree with your opinion. I'd like to use c++17 with my new project.
But sometimes, migrate an old project is really painful not even feasible.

[pantor]

Yeah, I feel you. Still, thanks for your input!

[davidchall]

@pantor - in case this affects your decision, I also need C++11 support. 😞

I have an R package called jinjar, which provides Jinja-like templating to the R community. This is a fairly academic community, and people often use older linux machines. C++11 is pretty standard there, but C++17 is still considered very futuristic 😆

[xiaozhuai]

@davidchall I've tried to replace all #include <string_view> with #include <nonstd/string_view.hpp> and std::string_view with nonstd::string_view. It works good!