[PATCH] D25124: Support rvalue references in enumerate range adapter.

[Zachary Turner via llvm-commits]

zturner added inline comments.


> zturner wrote in STLExtras.h:642-646
> The `remove_const` snuck in which I was tinkering around with things.  I need to remove that.  Thanks for pointing it out.
> 
> Correct me if I'm wrong here, but at least the conclusion I came to when trying to get this working was this:
> 
> 1. `std::declval<R>()` returns an `R&&`
> 2. `std::begin(R&&)` will select the overload of `std::begin()` that accepts a `const Container&`, because the result of `std::declval<R>()` is an rvalue, so it can't bind to the overload of `std::begin()` that accepts a `Container&`.
> 3. As a result, `std::begin()` returns a `const_iterator`.
> 4. This means `I` is typedefed to `std::vector<T>::const_iterator`, which will obviously not work for mutation.  (`vector` just an example since that's what i used in the tests, replace with arbitrary `R`).
> 
> By writing `std::declval<R&>()` you're forcing it to return an rvalue, so we get a non-const iterator (unless of course `R` is itself a const type)

The last sentence should say "By writing `std::declval<R&>()` you're forcing it to return an **lvalue**"

https://reviews.llvm.org/D25124