Is a container sure to be a range conceptually?

Question

From the documentation of ranges-v3:

view::all

Return a range containing all the elements in the source. Useful for converting containers to ranges.

What makes me confused are:

1. Under what scenarios are view::all used?
2. Are standard containers (std::vector, std::list, etc.) not ranges conceptually?

For example:

auto coll = std::vector{ 1, 2, 2, 3 };  
view::all(coll) | view::unique; // version 1
coll | view::unique; // version 2

Is there any difference between version 1 and version 2?

Answer 1

Egad, that part of the documentation hasn't been updated since range-v3 switched terminology. Yes, a container is a Range (it has begin() and end() that return an iterator/sentinel pair). It is not a View (a Range with O(1) copy/move). So, the documentation for view::all should read:

view::all

Return a View containing all the elements in the source. Useful for converting containers to Views.

To answer your second question, no there is no difference between version 1 and version 2 in your code.