feat(byteview): Add non-consuming mmap constructor

[flub]

This adds constructor to mmap a File into a ByteView without consuming
the file object.

[Swatinem]

So does mmap-ing keep the FD alive? Might be interesting to explicitly drop(file) after this, and see that the view still works (and holds on to the FD).

[flub]

Yes, mmap only uses the fd to figure out what to map, afterwards you can close it or do whatever you like to it. I added the explicit drop to make it even more obvious

[flub]

Yes,

That "yes" is not really true as the rest of the sentence explains 😄 mmap does not use the fd at all other than finding the right file to map. so it doesn't keep the FD alive either.

[loewenheim]

Since map_file only calls mmap_file internally anyway, is there a reason to keep both around? If we want to have both, I would propose naming them more distinctly; currently the names are very non-obvious and it's easy to read over the double m in mmap_file.

[flub]

Since map_file only calls mmap_file internally anyway, is there a reason to keep both around? If we want to have both, I would propose naming them more distinctly; currently the names are very non-obvious and it's easy to read over the double m in mmap_file.

Yeah, the naming is not ideal and I'm open to better suggestions.

I think API-wise we can't really change the behaviour of the existing method or remove it right away though.

[flub]

To be honest, I'm not overly concerned about the only naming difference being a single m even though that's easy to typo. The compiler will clearly make you chose the right one.